sonar _dr hatemelbitar00201005684344.pdf

m.i.t
academy
‫االكاديمية‬
‫الدولية‬
Sonography course Basic and advanced
00201005684344

introduction
This course is an educational tool
designed to assist practitioners in
providing appropriate diagnostic
knowledge to care for patients.
The practice of medicine involves not
only the science, but also the art of
dealing with the prevention,
diagnosis,alleviation, and treatment of
disease.

The variety and complexity of
human conditions make it
impossible to always reach the
most appropriate diagnosis or to
predict with certainty a particular
response to treatment.
Therefore, it should be recognized
that adherence to these practice
parameters will not assure an
accurate diagnosis or a successful
outcome.

All that should be expected is
that the practitioner will
follow a reasonable course of
action based on current
knowledge, available
resources, and the needs of
the patient to deliver effective

The clinical aspects contained in specific
sections of this practice parameter
(Introduction, Classification of Fetal
Sonographic Examinations, Specifications
of the Examination, Equipment
Specifications, and Fetal Safety) were
revised collaboratively by the American
College of Radiology (ACR), the American
Institute of Ultrasound in Medicine
(AIUM), the American College of
Obstetricians and Gynecologists (ACOG),
and the Society of Radiologists in
Ultrasound (SRU).

Recommendations for
physician qualifications,
written request for the
examination, procedure
documentation, and quality
control vary among the
organizations and are
addressed by each separately.
This practice parameter has
been developed for use by
practitioners performing
obstetrical sonographic studies.

Fetal ultrasound should be
performed only when there is a valid
medical reason, and the lowest
possible ultrasonic exposure settings
should be used to gain the necessary
diagnostic information .A limited
examination may be performed in
clinical emergencies or for a limited
purpose such as evaluation of fetal or
embryonic cardiac activity, fetal
position, or amniotic fluid volume.

A limited follow-up examination may be
appropriate for re-evaluation of fetal size or
interval growth or to re-evaluate
abnormalities previously noted if a
complete prior examination is on record.
While this practice parameter describes the
key elements of standard sonographic
examinations in the first trimester and
second and third trimesters, a more detailed
anatomic examination of the fetus may be
necessary in some cases, such as when an
abnormality is found or suspected on the
standard examination or in pregnancies at
high risk for fetal anomalies.

In some cases, other specialized
examinations may be necessary as
well.
While it is not possible to detect
all structural congenital anomalies
with diagnostic ultrasound,
adherence to the
following practice parameters will
maximize the possibility of
detecting many fetal
abnormalities.

CLASSIFICATION
OF FETAL
SONOGRAPHIC
EXAMINATIONS

A. First Trimester
Ultrasound Examination
A standard obstetrical sonogram in the first trimester
includes evaluation of the presence, size, location, and
number of gestational sac(s). The gestational sac is
examined for the presence of yolk sac and embryo/fetus.
When an embryo/fetus is detected, it should be measured
and cardiac activity recorded by 2D video clip or Mmode.
Use of spectral Doppler is discouraged. The uterus, cervix,
adnexa, and culde sac region should be
examined.

A standard obstetrical sonogram in the second
or third trimester includes an evaluation of
fetal presentation, amniotic fluid volume,
cardiac activity, placental position, fetal
biometry, and fetal number, plus an anatomic
survey. The maternal cervix and adnexa should
be examined as clinically appropriate when
technically feasible.
B. Standard Second or Third
Trimester Examination

A limited examination is performed when a
specific question requires investigation. For
example, in most routine nonemergency cases a
limited examination could be performed to
confirm fetal heart activity in a bleeding patient,
or to verify fetal presentation in a laboring
patient. In most cases limited sonographic
examinations are appropriate only when a prior
complete examination is on record.
C. Limited Examination

A detailed anatomic examination is performed
when an anomaly is suspected on the basis of
history, biochemical abnormalities, or the
results of either the limited or standard scan.
Other specialized examinations might include
fetal Doppler ultrasound, biophysical profile,
fetal echocardiogram, or additional biometric
measurements.
D. Specialized Examinations

WRITTEN REQUEST FOR
THE EXAMINATION
The written or electronic request for an
obstetrical ultrasound examination should
provide sufficient information to
demonstrate the medical necessity of the
examination and allow for its proper
performance and interpretation.
Documentation that satisfies medical
necessity includes 1) signs and symptoms
and/or 2)

WRITTEN REQUEST FOR
THE EXAMINATION
relevant history (including known diagnoses). Additional
information regarding the specific reason for the
examination or a provisional diagnosis would be helpful
and may at times be needed to allow for the proper
performance and interpretation of the examination. The
request for the examination must be originated by a
physician or other appropriately licensed health care
provider. The accompanying clinical information should be
provided by a physician or other appropriately licensed
health care provider familiar with the patient’s clinical
problem or question and consistent with the state’s scope
of practice requirements

SPECIFICATIONS
OF THE
EXAMINATION

A. First Trimester
1. Indications
Indications for first trimester3 sonography include:
a. Confirmation of the presence of an intrauterine pregnancy .
b Evaluation of a suspected ectopic pregnancy .
c. Defining the cause of vaginal bleeding.
d. Evaluation of pelvic pain.
e. Estimation of gestational (menstrual4) age.
f. Diagnosis or evaluation of multiple gestations.
g. Confirmation of cardiac activity.

A. First Trimester
1. Indications
Indications for first trimester3 sonography include:
h. Imaging as an adjunct to chorionic villus sampling, embryo transfer, and
localization and removal of
an intrauterine device (IUD).
i. Assessing for certain fetal anomalies, such as anencephaly, in high risk patients.
j. Evaluation of maternal pelvic masses and/or uterine abnormalities.
k. Measuring the nuchal translucency (NT) when part of a screening program for
fetal aneuploidy.
l. Evaluation of suspected hydatidiform mole

A. First Trimester
Scanning in the first trimester may be
performed either transabdominally
or transvaginally.
If a transabdominal examination is
not definitive, a transvaginal scan or
transperineal scan should be
performed whenever possible
2. Imaging
parameters

A. First Trimester
a. The uterus, (including the cervix),
and adnexa should be evaluated for the
presence of a gestational
sac. If a gestational sac is seen, its
location should be documented. The
gestational sac should be
evaluated for the presence or absence
of a yolk sac or embryo, and the crown-
rump length should be
recorded, when possible

A definitive diagnosis of intrauterine pregnancy can
be made when an intrauterine gestational sac
containing a yolk sac or embryo/fetus with cardiac
activity is visualized. A small, eccentric intrauterine
fluid collection with an echogenic rim can be seen
before the yolk sac and embryo are detectable in a
very early intrauterine pregnancy. In the absence of
sonographic signs of ectopic pregnancy, the fluid
collection is highly likely to represent an intrauterine
gestational sac. In this circumstance, the
intradecidual sign may be helpful.
a. The uterus

Follow-up sonography and/or serial determination of maternal
serum HCG (human chorionic gonadotropin) levels are appropriate
in pregnancies of undetermined location to avoid inappropriate
intervention in a potentially viable early pregnancy.
The crown-rump length is a more accurate indicator of gestational
(menstrual) age than is mean gestational sac diameter. However,
the mean gestational sac diameter may be recorded when an
embryo is not identified.
Caution should be used in making the presumptive diagnosis of a
gestational sac in the absence of a
definite embryo or yolk sac. Without these findings an intrauterine
fluid collection could represent a pseudo-gestational sac associated
with an ectopic pregnancy
a. The uterus

b. Presence or absence of cardiac
activity should be documented with 2D
video clip or M-mode.
With transvaginal scans, while cardiac
motion is usually observed when the
embryo is 2 mm or greater in length, if an
embryo less than 7 mm in length is seen
without cardiac activity, a subsequent
scan in one week is recommended to
ensure that the pregnancy is nonviable

c. Fetal number should be
documented.
Amnionicity and
chorionicity should be
documented for all multiple
gestations when possible.

d. Embryonic/fetal anatomy appropriate
for the first trimester should be assessed.
For those patients desiring to assess their
individual risk of fetal aneuploidy, a very
specific measurement of the NT during a
specific age interval is necessary (as
determined by the laboratory used). See the
guidelines for this measurement below.
e. The nuchal region should be imaged, and
abnormalities such as cystic hygroma should be
documented.

NT measurements should be used (in conjunction
with serum biochemistry) to determine the risk for
having a fetus with aneuploidy or other anatomical
abnormalities such as heart defects.
In this setting, it is important that the practitioner
measure the NT according to established guidelines
for measurement. A quality assessment program is
recommended to ensure that false-positive and
false-negative results are kept to a minimum
e. The nuchal region should be imaged, and
abnormalities such as cystic hygroma should be
documented.

i. The margins of the NT edges must be clear
enough for proper placement of the calipers.
ii. The fetus must be in the midsagittal plane.
iii. The image must be magnified so that it is
filled by the fetal head, neck, and upper
thorax.
Guidelines for NT measurement:

iv. The fetal neck must be in a neutral
position – not flexed and not
hyperextended.
v. The amnion must be seen as separate
from the NT line.
vi. The (+) calipers on the ultrasound must
be used to perform the NT measurement.

vii. Electronic calipers must be placed on
the inner borders of the nuchal line with
none of the horizontal crossbar itself
protruding into the space.
viii. The calipers must be placed
perpendicular to the long axis of the
fetus.

sonar _dr hatemelbitar00201005684344.pdf

Nuchal
translucency
“Nuchal translucency translucency-based
screening for fetal abnormalities has truly
become an indispensable aspect of
contemporary obstetric practice.”
(dr.Soha Said, Clinical Obstetrics and Gynecology, March 2008)

Topics:
Definition of Nuchal Translucency
Measurement Criteria NT in Trisomy 21
Screening Advantages/Limitations of NT
Screening Differential Diagnosis of Increased NT
Mechanisms of Increased NT Fetal Anomalies associated with Increased NT
Follow-up on Our Patients

f. The uterus including the cervix,
adnexal structures, and cul-de-sac
Abnormalities should be imaged and
documented.The presence, location, appearance,
and size of adnexal masses should be documented.
The presence and number of leiomyomata should
be documented. The measurements of the largest
or any potentially clinically significant leiomyomata
should be documented. The cul-de-sac should be
evaluated for the presence or absence of fluid.
Uterine anomalies should be documented.

Indications for second and third trimester sonography include, but are not limited to:
a. Screening for fetal anomalies .
b. Evaluation of fetal anatomy.
c. Estimation of gestational (menstrual) age.
d. Evaluation of fetal growth.
e. Evaluation of vaginal bleeding.
f. Evaluation of abdominal or pelvic pain.
g. Evaluation of cervical insufficiency.
h. Determination of fetal presentation.
i. Evaluation of suspected multiple gestation.
j. Adjunct to amniocentesis or other procedure.
k. Evaluation of significant discrepancy between uterine size and clinical dates.
l. Evaluation of pelvic mass.
B. Second and Third Trimester
1. Indications

Indications for second and third trimester sonography include, but are not limited to:
m. Evaluation of suspected hydatidiform mole.
n. Adjunct to cervical cerclage placement.
o. Suspected ectopic pregnancy.
p. Suspected fetal death.
q. Suspected uterine abnormality.
r. Evaluation of fetal well-being.
s. Suspected amniotic fluid abnormalities.
t. Suspected placental abruption.
u. Adjunct to external cephalic version.
v. Evaluation of premature rupture of membranes and/or premature labor.
w. Evaluation of abnormal biochemical markers.
x. Follow-up evaluation of a fetal anomaly.
y. Follow-up evaluation of placental location for suspected placenta previa.
z. History of previous congenital anomaly.
1. Indications

Abnormal heart rate and/or rhythm should be
documented. Multiple gestations require the
documentation of additional information:
chorionicity, amnionicity,comparison of fetal
sizes, estimation of amniotic fluid volume
(increased, decreased, or normal) in each
gestational sac, and fetal genitalia (when
visualized).
a. Fetal cardiac activity, fetal number, and presentation should be documented.

Although it is acceptable for experienced
examiners to qualitatively estimate
amniotic fluid volume, semi quantitative
methods have also been described for this
purpose (e.g., amniotic fluid index, single
deepest pocket, two-diameter pocket)
2. Imaging
parameters
b. A qualitative or semi quantitative estimate of amniotic fluid volume should be
documented.

The umbilical cord should be imaged, and the number of vessels in the cord documented. The
placental cord insertion site .should be documented when technically possible .
It is recognized that apparent placental position early in pregnancy may not correlate well with its
location at the time of delivery.
Transabdominal, transperineal, or transvaginal views may be helpful in visualizing the internal
cervical os and its relationship to the placenta.
Transvaginal or transperineal ultrasound may be considered if the cervix appears shortened or cannot
be adequately visualized during the transabdominal sonogram [29,30].
A velamentous (also called membranous) placental cord insertion that crosses the internal os of the
cervix is vasa previa, a condition that has a high risk of fetal mortality if not diagnosed prior to labor
2. Imaging
parameters
c. The placental location, appearance, and relationship to the internal cervical os
should be documented.

First-trimester crown-rump measurement is the most accurate
means for sonographic dating of pregnancy. Beyond this period, a
variety of sonographic parameters such as biparietal diameter,
abdominal circumference, and femoral diaphysis length can be
used to estimate gestational (menstrual) age. The variability of
gestational (menstrual) age estimation, however, increases with
advancing pregnancy. Significant discrepancies between
gestational (menstrual) age and fetal measurements may suggest
the possibility of fetal growth abnormality, intrauterine growth
restriction, or macrosomia
2. Imaging
parameters
d. Gestational (menstrual) age assessment

The pregnancy should not be redated after an accurate
earlier scan has been performed and is
available for comparison.
i. Biparietal diameter is measured at the level of the
thalami and cavum septi pellucidi or columns of the fornix.
The cerebellar hemispheres should not be visible in this
scanning plane. The measurement is taken from the outer
edge of the proximal skull to the inner edge of the distal
skull.
2. Imaging
parameters

The head shape may be flattened (dolichocephaly) or
rounded (brachycephaly) as a normal variant. Under these
circumstances, certain variants of normal fetal head
development may make measurement of the head
circumference more reliable than biparietal diameter for
estimating gestational (menstrual) age.
ii. Head circumference is measured at the same level as the
biparietal diameter, around the outer perimeter of the
calvarium. This measurement is not affected by head shape.
2. Imaging
parameters

iii. Femoral diaphysis length can be reliably used after 14 weeks
gestational (menstrual) age. The long axis of the femoral shaft is
most accurately measured with the beam of insonation being
perpendicular to the shaft, excluding the distal femoral epiphysis.
iv. Abdominal circumference or average abdominal diameter
should be determined at the skin line on a true transverse view at
the level of the junction of the umbilical vein, portal sinus, and
fetal stomach when visible. Abdominal circumference or average
abdominal diameter measurement is used with other biometric
parameters to estimate fetal weight and may allow detection of
intrauterine growth restriction or macrosomia.
2. Imaging
parameters

Fetal weight can be estimated by obtaining
measurements such as the biparietal diameter, head
circumference, abdominal circumference or average
abdominal diameter, and femoral diaphysis
length. Results from various prediction models can
be compared to fetal weight percentiles from
published nomograms
e. Fetal weight estimation

If previous studies have been performed,
appropriateness of growth should also be
documented.
Scans for growth evaluation can typically be
performed at least 2 to 4 weeks apart. A shorter
scan interval may result in confusion as to whether
measurement changes are truly due to growth as
opposed to variations in the technique itself.

Currently, even the best fetal weight prediction
methods can yield errors as high as ±15
percent. This variability can be influenced by
factors such as the nature of the patient
population, the number and types of anatomic
parameters being measured, technical factors
that affect the resolution of ultrasound images,
and the weight range being studied.

Evaluation of the uterus, adnexal structures, and cervix should
be performed when appropriate. If the cervix cannot be
visualized, a transperineal or transvaginal scan may be
considered when evaluation of the cervix is needed.This will
allow recognition of incidental findings of potential clinical
significance. The presence,location, and size of adnexal masses
and the presence of at least the largest and potentially clinically
significant leiomyomata should be documented. It is not always
possible to image the normal maternal ovaries during the
second and third trimesters.
f. Maternal anatomy

• g. Fetal anatomic survey
• Fetal anatomy, as described in this document, may be
adequately assessed by ultrasound after
approximately 18 weeks gestational (menstrual) age. It may
be possible to document normal structures before this time,
although some structures can be difficult to visualize due to
fetal size,position, movement, abdominal scars, and increased
maternal abdominal wall thickness]. Asecond or third
trimester scan may pose technical limitations for an anatomic
evaluation due to imaging artifacts from acoustic shadowing.
When this occurs, the report of the sonographic examination
should document the nature of this technical limitation. A
follow-up examination may be helpful.
2. Imaging
parameters

• g. Fetal anatomic survey
• The following areas of assessment represent the minimal elements of a standard
examination of fetal anatomy. A more detailed fetal anatomic examination may be
necessary if an abnormality or
• suspected abnormality is found on the standard examination.
• i. Head, face, and neck
• Lateral cerebral ventricles
• Choroid plexus
• Midline falx
• Cavum septi pellucidi
• Cerebellum
• Cistern magna
• Upper lip
• A measurement of the nuchal fold may be helpful during a specific age interval to
assess the risk of
• aneuploidy

REFERENCES
1. Barnett SB, Ter Haar GR, Ziskin MC, Rott HD, Duck FA, Maeda K. International recommendations and
guidelines for the safe use of diagnostic ultrasound in medicine. Ultrasound Med Biol 2000;26:355-366.
2. Bly S, Van den Hof MC. Obstetric ultrasound biological effects and safety. J Obstet Gynaecol Can
2005;27:572-580.
3. Barnhart K, van Mello NM, Bourne T, et al. Pregnancy of unknown location: a consensus statement of
nomenclature, definitions, and outcome. Fertil Steril 2011;95:857-866.
4. Jeve Y, Rana R, Bhide A, Thangaratinam S. Accuracy of first-trimester ultrasound in the diagnosis of early
embryonic demise: a systematic review. Ultrasound Obstet Gynecol 2011;38:489-496.
5. Thilaganathan B. The evidence base for miscarriage diagnosis: better late than never. Ultrasound Obstet
Gynecol 2011;38:487-488.
6. Chambers SE, Muir BB, Haddad NG. Ultrasound evaluation of ectopic pregnancy including correlation with
human chorionic gonadotrophin levels. Br J Radiol 1990;63:246-250.
7. Hill LM, Kislak S, Martin JG. Transvaginal sonographic detection of the pseudogestational sac associated
with ectopic pregnancy. Obstet Gynecol 1990;75:986-988.
8. Kirk E, Daemen A, Papageorghiou AT, et al. Why are some ectopic pregnancies characterized as pregnancies
of unknown location at the initial transvaginal ultrasound examination? Acta Obstet Gynecol Scand
2008;87:1150-1154.
9. Laing FC, Frates MC. Ultrasound evaluation during the first trimester of pregnancy. In: Ultrasonography in
obstetrics and gynecology. 4th ed. Philadelphia, PA: WB Saunders; 2000:105-145.

Guidelines for
the Performance
of First Trimester
Ultrasound

• Studies should be performed using an abdominal
and/or vaginal approach. A high frequency
transducer should be used and the equipment
should be operated with the lowest ultrasonic
exposure settings capable of providing the
necessary diagnostic information. A vaginal
transducer should always be available and a
transvaginal scan should be offered to the patient
when it is anticipated that this would result in a
more diagnostic study. The patient may choose to
accept or refuse this offer and undue persuasion
is inappropriate.

GESTATION SAC
• The gestation sac should usually be visible from
four and one half (4.5) to five (5) weeks using
high frequency transvaginal ultrasound.
• When a gestation sac like structure is seen but no
live fetus demonstrated, it is important to
attempt to ensure that it is not a 'pseudo
gestational sac'. Look for the echogenic
trophoblast rim and the yolk sac, and ensure that
the fluid in the gestation sac is echo free.

• If a gestation sac is not visible in the uterus of a
patient believed to be pregnant, the adnexa
should be carefully examined looking for evidence
suggesting the presence of an ectopic pregnancy -
most ectopics can be suspected with high
frequency transvaginal ultrasound.
• In a patient with a positive pregnant test but
either -
• • no gestational sac is seen within the uterus or
elsewhere in the pelvis
• • an apparent sac is seen but no fetal structures
(including yolk sac) or heart movements are
visible

GESTATIONAL AGE
• This is most accurately assessed in the first
trimester. The earlier the crown rump length
(CRL) is measured, the more accurate is the
assessment of gestational age. The CRL can be
measured from six weeks gestation. The
composite CRL chart in the ASUM Policies and
Statements folder is recommended. From
eleven weeks multiparameter assessment can
be used. Biparietal diameter (BPD) is the most
often used second measurement

FETAL HEART MOVEMENTS
• With a high resolution vaginal
transducer, fetal heart movements
are often visible from five (5) to six
(6) weeks (i.e. CRL = 2mm), but may
not be seen until CRL = 3-4mm

PREGNANCY FAILURE
• An experienced operator using high quality transvaginal equipment
may diagnose pregnancy failure under either or both of the
following circumstances:
• 1. When no live fetus is visible in a gestation sac and the mean sac
diameter (MSD) cut off >25mm.
• 2. When there is a visible fetus with a CRL cut off >7mm but no fetal
heart movements can be demonstrated. The area of the fetal heart
should be observed for a prolonged period of at least thirty (30)
seconds to ensure that there is no cardiac activity.
• In situations where pregnancy failure is suspected by an operator
who either does not have extensive experience in making the
diagnosis or does not have access to high quality equipment or if
there is any doubt about the viability of the fetus, a second opinion
or a review scan in one week .

NUCHAL TRANSLUCENCY
• The nuchal translucency measurement is a test to
assess the risk of chromosomal abnormality, in
particular of trisomy 21. The measurement may
also be abnormal in other fetal anomalies (e.g.
some congenital heart disease). It has been
estimated that first trimester screening by a
combination of sonography and material serum
testing of PAPP-A and free βhCG can potentially
identify 94% of trisomy 21 fetuses with a false
positive rate of 5%.

• The nuchal translucency
measurement may be performed at
the request of the referring Medical
Practitioner. Due consideration
should be given as to how and who is
going to counsel the patient prior to
the performance of a nuchal
translucency scan.

• Method of measurement:
• 1. The nuchal translucency should be measured
on a sagittal midline scan through the fetus.
• 2. The fetus should be in neutral position and
occupy at least 75% of the image.
• 3. The amnion should be seen separate to the
fetal skin line.
• 4. Calipers should be positioned to measure
the maximum diameter of the fluid at the back
of the neck.

OVARIES, UTERUS AND ADNEXA
• Each ovary should be examined. The corpus
luteum can vary greatly in appearance during
the first (and early second) trimesters of
pregnancy. Sonographic appearances include a
solid, rounded target like lesion or a
predominately cystic structure. Peripheral
vascularity is usually detectable.
• The size of a corpus luteum is also variable,
commonly measuring up to 3cm.

• Larger or unusual masses should
assessed as in the non pregnant
woman.
• The uterus should be examined for
evidence of a fibroids or uterine
developmental defects. The uterine
position should also be noted
(anteverted, axial, retroverted).
• The adnexa should be examined for
coexistent ectopics and free fluid.

REFERENCES
• 1. Hately, Case and Campbell. Establishing the
death of an embryo by ultrasound. Ultrasound
Obstet. Gynecol.5 (1995) 353-357
• 2. Nicolaides KH Am. J. Obstet. Gynecol.
(2004) 191:45-47
• 3. From Nicolaides group: Snijders et al.
Assessmant of risk of Trisomy 21 by maternal
age and fetal nuchal-translucency thickness.

• Antenatal fetal monitoring is a routine part of
antenatal care in that fetal growth is assessed by
palpation of uterine and enquiries as to
• whether the baby is active assess fetal wellbeing.
These take place at every antenatal check. In most
pregnancies this is an adequate measure of fetal
well being but on occasions when there is concern
regarding a specific aspect of fetal wellbeing more
detailed monitoring is necessary.

Indications
Situations which may
require more detailed
fetal monitoring
include:

A. Maternal hypertension
• Hypertension in pregnancy is not a single entity but
comprises:
• Chronic (essential) hypertension which complicates 1 –
5 % of pregnancies and is defined as a blood pressure
greater that 140/90 millimetres of mercury that either
pre-dates pregnancy or develops before 20 weeks of
gestation.
• Pregnancy induced hypertension which develops after
20 weeks of gestation and complicates 5 – 10% of
pregnancies
• Pre-eclampsia which is pregnancy induced hypertension
in association with proteinuria or oedema or both.

B. Reduced fetal activity
• The perception of fetal movement by an expectant
mother is extremely variable. However, during the
second half of pregnancy most women are aware of fetal
movements and can appreciate when the frequency of
movements reduces significantly. All women should be
asked to pay attention to the frequency of fetal
movements during the latter stages of pregnancy. This is
however, particularly important where there has been an
adverse outcome to a previous pregnancy or where
there is a suspicion of intrauterine growth restriction in
the present pregnancy. 55% of women experiencing a
still birth had perceived a reduction of fetal movements
prior to the diagnosis.

C. Suspected small for gestational age (SGA) fetus
• The absolute size of a baby at any given gestation is an
unreliable indicator of health and well being. The
nearer to term the greater is the natural variation in
the size/weight of baby. Some will be constitutionally
smaller or larger than average. Others may be of an
average weight but not have reached the growth
potential for that particular fetus. For these reasons
the rate of growth is far more important than any one
single measurement. A series of ultrasound
measurements is therefore required which should be
plotted on the charts in the antenatal notes. Deviation
from the normal growth curve, particularly of the
abdominal circumference may be an indication of fetal
compromise.

D. Previous stillbirth / neonatal death
• Whether or not women are at increased risk of an
adverse outcome will depend upon the cause of
the previous stillbirth or neonatal death. Where
extreme prematurity is implicated strategies to
detect/prevent the onset of pre-term labour will
be required. Where unexplained fetal loss has
occurred late in pregnancy close monitoring and
elective delivery before term are usually advised.

E. Post maturity
• Patients where the pregnancy is still ongoing
more than 2 weeks after the agreed due date
but whose pregnancy is otherwise
uncomplicated require additional fetal
monitoring .Reasons for this may include: -
• Patient declines induction of labour
• No appointment slots are available for induction
of labour
• Cervix is unfavourable and patient and
obstetrician prefer to delay induction of labour.

ULTRASOUND
DIAGNOSIS
OF EARLY
PREGNANCY
MISCARRIAGE

The purpose of this guideline
•is to assist all healthcare
professionals in the
management of first
trimester spontaneous
miscarriage.

What is a Threatened Miscarriage?
• A threatened miscarriage is a pregnancy where vaginal
bleeding has taken place but an ultrasound has shown
a healthy fetus and fetal heartbeat. The bleeding can
be very varied and can occur at any time after a missed
period. It can range from being a smear of pink, brown
or red loss on the toilet paper to heavy vaginal
bleeding similar or even heavier than a period. The
diagnosis of a threatened miscarriage is made when
you attend for an ultrasound scan and as long as you
are at least 6 weeks pregnant the ultrasound should be
able to visualise your tiny baby and show a healthy
heartbeat. It may be necessary to demonstrate by
performing an internal vaginal scan.

• Sometimes the scan may show up a small
haematoma (blood clot) around the pregnancy
sac but very often nothing abnormal is seen
and it is difficult to explain why the bleeding
has occurred. The bleeding may have come
from the implantation site which is when the
placenta of your baby burrows itself into the
lining of the womb. This process may cause
some bleeding. If we can see a baby‟s
heartbeat on ultrasound it is very likely that
your pregnancy will continue with success rates
exceeding 95%.

• If there is a collection of blood around the pregnancy sac
or the bleeding continues, it may be appropriate to
repeat an ultrasound scan in 1-2 weeks. In any case the
heartbeat will be checked at your first booking visit in
the hospital. If the bleeding settles down there is
probably no need for a further scan unless you have
further anxieties. Traditionally bed rest has been advised
for mothers with threatened miscarriage but all the
evidence would suggest that this does not prevent
miscarriage. It may help some patients psychologically to
rest in bed but it is not necessary. Unfortunately there is
no specific treatment to stop the bleeding and if you do
adopt bed rest there is the possibility that on standing
up bleeding may become heavier due to pooling of
blood in the vagina that results from lying down.

• Spontaneous miscarriage is the commonest
complication of pregnancy. It occurs in up to 20% of
clinical pregnancies equating to approximately 15,000
miscarriages per annum in Ireland.
• This guideline provides information relating to the
diagnosis of early pregnancy loss defined as a loss,
within the first 13 weeks of pregnancy. It specifically
addresses the ultrasound diagnosis of miscarriage. This
guideline is intended to be primarily used by health
personnel working in the area of early pregnancy
which includes obstetricians, midwife sonographers,
radiographers, radiologists and general practitioners.
All of the groups should be familiar with the various
diagnostic tools necessary to help delineate a viable
from a non-viable pregnancy.

Ultrasound and Embryo Development
• It is important that all relevant health personnel
are familiar with the chronological ultrasound
features of early pregnancy. The first ultrasound
evidence of pregnancy is the gestational sac
within the thickened decidua. This sac which
represents the chorionic cavity is a small anechoic
fluid collection surrounded by an echogenic ring
that represents trophoblasts and decidual
reaction. It is possible to identify the sac with
transvaginal ultrasound by 4 weeks and 2 days
when the mean diameter is 2-3 mm.

• The yolk sac is the first structure often seen
within the gestational sac and it confirms an
intrauterine pregnancy. The yolk sac is first
seen by transvaginal ultrasound when the
mean gestational sac diameter is ≥5 mm, and
should always be visualised when the mean
gestational sac diameter is >7 mm. The amnion
is a thin, rounded membrane surrounding the
embryo and is completely enveloped by the
thick echogenic chorion.

• The yolk sac is situated between the amnion
and the chorion. The amnion is thin and difficult
to visualise and is best seen when perpendicular
to the ultrasound beam. The amnion grows
rapidly during pregnancy and fuses with the
chorion between 12 and 16 weeks gestation.
The embryo can be identified by transvaginal
ultrasound when as small as 1–2 mm in length.
At 5–7 weeks gestation both the embryo and
gestational sac should grow at approximately 1
mm per day.

• Cardiac activity immediately adjacent
to the yolk sac indicates a live embryo
but may not be seen until the embryo
measures 5 mm. From 5 ½ - 6 ½
weeks gestation a fetal heart rate of
less than 100 beats per minute is
normal. During the following 3 weeks
there is a rapid increase up to 180
beats per minute.

Ultrasound Determination of Pregnancy Loss
• If on transvaginal ultrasound, the mean
gestational sac diameter is less than 20mm
with no yolk sac or embryo, or if the fetal pole
is less than 8mm with no cardiac activity
identified within 30 seconds, then the
diagnosis of pregnancy of uncertain viability
may be made. A repeat ultrasound
examination should be arranged after 7-10
days to clarify the diagnosis.

• An ultrasound diagnosis of fetal demise may be
made when there is no fetal heart in a fetus with
fetal pole >7mm when using transvaginal
ultrasound. A diagnosis of pregnancy loss may also
be made if the mean gestational sac diameter
exceeds 20 mm in the absence of a yolk sac or
embryo. Particular care should be taken to scan all
of the sac in a longitudinal and vertical plain. The
mean sac diameter should be measured in 3
diameters and averaged. The area of the fetal heart
should be observed for a prolonged period of at
least 30 seconds to ensure that there is no cardiac
activity. The use of transvaginal ultrasound should
be encouraged as better visualisation is nearly
always possible.

• Different cutoffs for diagnosing miscarriage apply
when using transabdominal ultrasound. If
transvaginal ultrasound is not available or not
acceptable to a woman, transabdominal
ultrasound criteria for fetal demise can be made
when there is no fetal heart in an embryo
measuring >8 mm. Similarly, if the mean
gestational sac diameter is > 25 mm in the absence
of a yolk sac or embryo, a diagnosis of fetal demise
can be made using transabdominal ultrasound. If
there is no sign of either intra or extra-uterine
pregnancy or retained products in a woman with a
positive pregnancy test, this should be described
as a pregnancy of unknown location.

• It is not essential for a second sonographer to
confirm fetal demise, provided that the first
sonographer is appropriately qualified and has
adhered to the guidelines. It may be distressing for
the woman to undergo another unnecessary
transvaginal assessment. It should, however, be
emphasised that if there is any doubt in the
diagnosis, a second opinion should be sought. Also,
if a second opinion may benefit a woman
psychologically, it should be facilitated. It is
important to listen carefully to the views of the
woman, particularly in circumstances where she
has had a prior pregnancy.

Prediction of Early Pregnancy Failure
• There are certain ultrasound features which predict but
are not diagnostic of early pregnancy failure. These
include a fetal heart rate of less than 85 beats per
minute at greater than 7 weeks gestation, a small sac
size relative to the embryo (difference of less than 5
mm between gestation sac and crown rump length),
enlarged or abnormally shaped yolk sac and sub-
chorionic haematoma. The latter leads to a pregnancy
loss rate of about 9%. This risk would appear to be
increased in women older than 35 years and in
pregnancies less than 8 weeks gestation.
• Any clinical interventions, however, must be based on
diagnostic and not predictive features.

Common Pitfalls with Ultrasound in Early Pregnancy
• Exercise extreme caution with regard to last
menstrual period (LMP) on history taking. Up
to 50% of women are uncertain of their dates,
or have an irregular cycle, or have just stopped
the oral contraceptive pill (OCP), or are
lactating or did not have a normal last period
Enquire when the women had her first
positive pregnancy test (which may be
positive 3 days before the missed period).

• Visualise all of the uterus. Pan the uterus
in saggital, and then rotate the probe 90
degrees to visualise from cervix to fundus.
Failure to visualise all of the uterus will
result in missing gestational sacs in
multiple pregnancies.
• Neglecting to scan the adnexae will result
in missing hererotopic pregnancies and
ovarian masses which may require surgery.

• Avoid labelling subchorionic bleeds as
additional gestational sacs. Do not tell a
woman that she has a twin pregnancy with one
empty sac unless you are very experienced in
ultrasound.
• Pseudosacs. Exercise caution in labelling
intrauterine sac–like structures as gestational
sacs unless they have contents i.e. yolk sac or
fetus. Pseudosacs will follow the uterine cavity
and are more ellipitical, while gestational sacs
are fundal and eccentrically placed.

• Fibroid Uterus. The fundus of a
fibroid uterus may not be included in
the scan field at TVS. Both TVS and
abdominal scans are needed in these
women to avoid missing gestational
sacs.

Women who should be assessed
at an early pregnancy unit include:
• Those with a history of a positive pregnancy test and:
• Vaginal bleeding and / or abdominal pain
• Previous ectopic pregnancy
• Previous tubal surgery
• Previous miscarriage
• Intrauterine contraceptive device in situ
• Persistent bleeding post evacuation of the retained
products of conception (ERPC) where there is a
suspicion of problems
• Other clinical indications as agreed in each hospital

The sonographer should produce reports using standardised documentation.
This includes:
• Presence or absence of an intrauterine gestational
sac(s)
• Number of sacs and mean gestational sac size
• Presence of haematoma
• Yolk sac
• Fetal Pole
• Crown Rump Length (CRL) with expected gestation
• Fetal heart pulsation present or absent
• Extrauterine observation to include ovaries, adnexal
mass / fluid in the Pouch of Douglas

Three-dimensional Ultrasound
Imaging

Three-dimensional Ultrasound Imaging
Three-dimensional ultrasound (3DUS) has become an
increasingly important component of clinical imaging.
While early applications have been focused on cardiac,
obstetric, and gynecologic applications its capabilities
continue to expand throughout the clinical arena. This
expansion is driven by important improvements in
technology, image quality and clinical ease of use. This
chapter will provide a brief review of the technology
behind 3D and 4D ultrasound imaging, clinical
considerations in acquiring, displaying and analyzing
3D/4D ultrasound data and the clinical contributions
this exciting technology is making.

• Ultrasound is a versatile imaging technique that
can reveal the internal structure of organs, often
with astounding clarity.
• Ultrasound is unique in its ability to image patient
anatomy and physiology in real time, providing an
important, rapid and noninvasive means of
evaluation. Ultrasound continues to make
significant contributions to patient care by
reassuring patients and enhancing their quality of
life by helping physicians
• understand their anatomy in ways not possible
with other techniques.

• Three-dimensional ultrasound (3DUS) is an
increasingly important area of ultrasound
development . 3DUS exploits the real-time
capability of ultrasound to build a volume that
can then be explored using increasingly
affordable high performance workstations.
3DUS is a logical evolution of ultrasound
technology and complements other parallel
developments underway at this time, including
harmonic imaging and the development of
ultrasound contrast materials.

EQUIPMENT DESIGN
• Design of clinically useful scanning equipment is crucially
• dependent on having an easy-to-use system that provides rapid
feedback to the clinician user in a straightforward manner.
• While superb image quality is expected, it also is important
• to avoid an overabundance of bells and whistles that often
• distract and overwhelm users rather than enhance the clinical
• imaging experience. Fundamental to an optimal operational
• environment is a highly functional, ergonomically designed
• user interface (Fig. 1). Selection of scanner features should
• be task related, obvious and context dependent.

ACQUISITION APPROACHES
• Acquisition of a data volume requires significant
computing resources to process the acoustic and
position data rapidly and create a volume. Various
strategies are available in clinical scanners with
most directed toward providing ”real-time”
images to the clinical user.
• Among the primary approaches employed are
free-hand scanning with and without position
sensing, mechanical devices integrated into the
transducer and matrix array technology(Fig. 3).

DISPLAY STRATEGIES
• Visualization of the relevant patient anatomy
will ultimately determine the clinical utility of
3DUS. Although traditional methods of
viewing multi-planar images provide much
information , volume rendering for
visualization of underlying patient anatomy
including blood flow offers new ways to
visualize complex anatomy in a single image
and to enhance the visibility of structures that
previously were difficult to appreciate.

• Visualization depends on optimised algorithms
to display the structure of interest and fast
computing hardware to display the results fast
enough to interactively adjust parameters or
viewing orientation. Volume data currently are
displayed using two primary methods: these
are a series of multiplanar images (typically
three slices that are orthogonal to each
other),and rendered images that show entire
structures throughout the volume (Fig. 6).

In the fetus, improved visualization of fetal features,
including:
• the face and limbs, has improved anomaly identification and been
immediately appealing for clearly sharing development information
with the family.
• Cardiac applications have provided a surgeon’s eye view using
transesophageal and transthoracic techniques to assess valve
geometry and motion and to plan operative procedures.
• Fetal cardiac imaging has become an increasingly important part of
prenatal diagnosis as a result of the development of
• four-dimensional imaging methods Gynecological applications
include evaluating congenital anomalies of the uterus, endometrial
cancer, adnexal masses,intrauterine device position and follicular
cysts. With 3DUS, it is possible to obtain the coronal plane of the
uterus (Fig. 11), which is not possible with 2DUS. This view greatly
facilitates identification of uterine anatomy, which can be important
in managing infertility and congenital anomalies

What are 3D and
4D ultrasound
scans?

3D scans show still
pictures of your baby in
three dimensions. 4D
scans show moving 3D
images of your baby,
with time being the
fourth dimension.
It's natural to be really
excited by the prospect
of your first scan. But
some mums find the
standard 2D scans
disappointing when all
they see is a grey, blurry
outline. This is because
the scan sees right
through your baby, so
the photos show her
internal organs.

With 3D and 4D scans, you see
your baby's skin rather than her
insides. You may see the shape
of your baby's mouth and nose,
or be able to spot her yawning
or sticking her tongue out.

-3D and 4D scans are considered as safe as 2D
scans, because the images are made up of
sections of two-dimensional images converted
into a picture. However, experts do not
recommend having 3D or 4D scans purely for a
souvenir photo or recording, because it means
that you are exposing your baby to more
ultrasound than is medically necessary. Some
private ultrasounds can be as long as 45
minutes to an hour, which may be longer than
recommended safety limits.

3D and 4D scans may nonetheless provide more
information about a known abnormality. Because
these scans can show more detail from different
angles, they can help in the diagnosis of cleft lip.
This can help doctors to plan the repair after birth.
3D scanning can also be useful to look at the heart
and other internal organs. As a result, some fetal
medicine units do use 3D scans, but only when
they're medically necessary.

There’s no evidence to suggest that the scans
aren’t safe, and most mums-to-be gain
reassurance from them. Nonetheless, any type
of ultrasound scan should only be performed by
a trained professional, for as short a time and at
the lowest intensity, as possible.
If you’d like a 3D or 4D scan you’ll probably
need to arrange it privately, and pay a fee. The
clinic may also give you a recording of the scan
on DVD, though this is likely to cost extra.

The special transducers and software required to
do 3D and 4D scans are expensive. There are few
clear medical benefits, and experts say they
should only be done if there's a medical need. So
it's unlikely that these scans will replace normal
2D scans used for routine maternity care in the
NHS.
If you decide to have one, the best time to have a
3D or 4D scan is when you're between 26 weeks
and 30 weeks pregnant.

Before 26 weeks your baby has very little fat under
her skin, so the bones of her face will show through.
After 30 weeks, your baby's head may go deep
down in your pelvis, so you may not be able to see
her face.
If the placenta is at the front of your womb (uterus),
known as anterior placenta, you'll get the best
images of your baby if you wait until 28 weeks.
It's natural that you'd like to see your baby's face on
the scan. But sometimes it's not possible,
depending on how she's lying.

-If she's lying facing outwards, with a good pool of
amniotic fluid around her features, you should be able to
see her face clearly. But if she's facing your back, her
head's far down in your pelvis, or there's not much fluid
around her, you won't see much. The same applies if you
have a lot of tummy fat.
-The sonographer may ask you to go for a walk, or to
come back in a week, when your baby may have moved
to a better position. If it's not possible to get good views
of her face, you may be able to see her fingers and toes
instead.

3D and 4D ultrasound in fetal cardiac
scanning

• Over the last decade we have been witness to
a burgeoning literature on three-dimensional
(3D) and four-dimensional (4D) ultrasound-
based studies of the fetal cardiovascular
system. Recent advances in the technology of
3D/4D ultrasound systems allow almost real-
time 3D/4D fetal heart scans.

• It appears that 3D/4D ultrasound in fetal
echocardiography may make a significant
contribution to interdisciplinary
management team consultation, health
delivery systems, parental counseling, and
professional training. Our aim is to review
the state of the art in 3D/4D fetal
echocardiography through the literature
and index cases of normal and anomalous
fetal hearts.

• Three-dimensional (3D) and four-
dimensional (4D) applications in fetal
ultrasound scanning have made
impressive strides in the past two
decades. Today, many more centers
have 3D/4D ultrasound capabilities at
their command ,and we are witness to a
burgeoning literature of 3D/4Dbased
studies.

• Perhaps in no other organ system is this recent
outstanding progress so evident as in the fetal
cardiovascular system. Recent technological
developments of motion-gated cardiac scanning
allow almost real-time 3D/4D heart examination.
• It appears from this growing body of literature
that 3D/4D ultrasonography can make a
significant contribution to our understanding of
the developing fetal heart in both normal
• and anomalous cases, to interdisciplinary
management team consultation, to parental
counseling, and to professional training.

• These features may work to extend the
benefits of prenatal cardiac screening to
poorly-served areas.
• The introduction of ‘virtual planes’ to fetal
cardiac scanning has helped sonographers
obtain views of the fetal heart not generally
accessible with a standard two-dimensional
(2D) approach.

• It is perhaps too early to evaluate whether 3D/4D
cardiac scanning will improve the accuracy of
fetal echocardiography programs.
• However, there is no doubt that 3D/4D
ultrasonography gives us another look at the fetal
heart. The purpose of this review is to summarize
the recent technological advances in 3D/4D fetal
echocardiography , demonstrating their
application through normal and anomalous
cases.

3D/4D TECHNIQUES AND THEIR
APPLICATION TO FETAL CARDIAC
SCANNING
• Spatio-temporal image correlation (STIC)
• STIC acquisition is an indirect motion-gated offline scanning
mode1–4. The automated volume acquisition is made possible by
the array in the transducer performing a slow single sweep,
recording a single 3D data set consisting of many 2D frames one
behind the other.
• The volume of interest (VOI) is acquired over a period of about 7.5
to 30 s at a sweep angle of approximately 20–40◦ (depending on
the size of the fetus) and frame rate of about 150 frames per
second. A 10-second, 25◦acquisition would contain 1500 B-mode
images4. Following acquisition the ultrasound system applies
• mathematical algorithms to process the volume data and detect
systolic peaks, which are used to calculate the fetal heart rate.

• The B-mode images are arranged in order
according to their spatial and temporal
domain, correlated to the internal trigger, the
systolic peaks that define the heart cycle4
(Figure 1).

• The resultant 40 consecutive volumes are a
reconstructed complete heart cycle that displays
in an endless loop.
• This cine-like file of a beating fetal heart can be
manipulated to display any acquired scanning
plane at any stage in the cardiac cycle (Figure 2).
• While a complex process to describe, this
reconstruction takes place directly following the
scan in a matter of seconds;

• the STIC acquisition can be reviewed with the
patient still present and repeated if necessary, and
saved to the scanning machine or a network.
Optimal STIC acquisition technique for examination
of the fetal heart is thoroughly.
• In post-processing, various methodologies have
been proposed to optimize the acquisition to
demonstrate the classic planes of fetal
echocardiography (Figure 3), as well as ‘virtual
planes’ that are generally inaccessible in 2D cardiac
scanning.

• These views once obtained are likewise stored in the
patient’s file, in addition to the original volume,
either as static images or 4D motion files. Any of the
stored information can be shared for expert review,
interdisciplinary consultation, parental counseling, or
teaching.
• STIC is an acquisition modality that can be combined
with other applications by selecting the appropriate
setting before acquisition (B-flow, color and power
Doppler, tissue Doppler, high-definition flow Doppler)
or with post processing visualization modalities (3D
volume rendering, inversion mode, tomographic
ultrasound imaging).

• By moving the point the operator manipulates the
volume to display any plane within the volume; if
temporal information was acquired, the same plane
can be displayed at any stage of the scanned cycle.
• From a good STIC acquisition the operator can
scroll through the acquired volume to obtain
sequentially each of the classic five planes6 of fetal
echocardiography, and any plane may be viewed at
any time-point throughout the reconstructed
cardiac cycle loop. The cycle can be run or stopped
frame-by-frame to allow examination of all phases
of the cardiac cycle, for example opening and
closing of the atrioventricular valves.

• By comparing the A- and B-frames of the MPR
display, the operator can view complex cardiac
anatomy in corresponding transverse and
longitudinal planes simultaneously. So, for example,
an anomalous vessel that might be disregarded in
cross-section is confirmed in the longitudinal plane.
• 3D rendering is another analysis capability of an
acquired volume. It is familiar from static 3D
applications, such as imaging the fetal face in surface
rendering mode. In fetal echocardiography it is
readily applied to 4D scanning.

• The operator places a bounding box around the region of
interest within the volume (after arriving at the desired
plane and time) to show a slice of the volume whose depth
reflects the thickness of the slice.
• For example, with the A-frame showing a good four
chamber view, the operator places the bounding box tightly
around the interventricular septum. The rendered image in
the D-frame will show an ‘en face’ view of the septum. The
operator can determine whether the plane will be
displayed from the left or right, i.e. the septum from within
the left or the right ventricle; the thickness of
• the slice will determine the depth of the final image, for
example to show texture of the trabeculations within the
right ventricle (Figure 4).

• TUI is a more recent application that extends the
capabilities of MPR and rendering modes. This multislice
analysis mode resembles a magnetic resonance imaging
or computer-assisted tomography display. Nine parallel
slices are displayed simultaneously from the plane of
interest (the ‘zero’ plane), giving sequential views from
−4 to +4. The thickness of the slices, i.e. the distance
between one plane and the next, can be adjusted by the
operator. The upper left frame of the display shows the
position of each plane within the region of interest,
relative to the reference plane. This application has the
advantage of displaying sequential parallel planes
simultaneously, giving amore complete picture of the
fetal heart (Figure 5).

• 3D/4D with color Doppler, 3D power Doppler (3DPD)
and 3D high definition power flow Doppler Color and
power Doppler have been extensively applied to fetal
echocardiography; one could hardly imagine
performing a complete fetal echo scan today without
color Doppler. Color or power Doppler, and the most
recent development, high definition flow Doppler, can
be combined with static 3D direct volume non-gated
scanning to obtain a 3D volume file with color Doppler
information or 3DPD (one-color) volume files.
• Color Doppler can be used more effectively in 3D/4D
ultrasonography when combined with STIC
acquisition12 in fetal echocardiography, resulting in a
volume file that reconstructs the cardiac cycle, as
above, with color flow information.

• This joins the Doppler flow to cardiac events2 and
provides all the advantages of analysis (MPR,
rendering, TUI) with color. This combination of
modalities is very sensitive for detecting intracardiac
Doppler flow through the cardiac cycle, for example
mild tricuspid regurgitation that occurs very early in
systole or very briefly can be clearly seen.
• Extreme care must be taken when working with
Doppler applications in post-processing, however, to
avoid misinterpretation of flow direction as the volume
is rotated.

• 3DPD is directionless, one-color Doppler that is
most effectively joined with static 3D scanning2.
3DPD uses Doppler shift technology to reconstruct
the blood vessels in the VOI, isolated from the rest
of the volume. Using the ‘glass body’ mode in post-
processing, surrounding tissue is eliminated and the
vascular portion of the scan is available in its
entirety for evaluation. The operator can scroll
spatially to any plane in the volume (but not
temporally: in this case, color Doppler with STIC is
more effective, see above).

• 3DPD can reconstruct the vascular tree of the
fetal abdomen and thorax14,15, relieving the
operator of the necessity of reconstructing
amental picture of the idiosyncratic course of an
anomalous vessel from a series of 2D planes.
• This has been shown to aid our
• understanding of the normal and anomalous
anatomy and pathophysiology of vascular
lesions16 (Figure 6).

• High-definition power flow Doppler, the newest
development in color Doppler applications, uses
high resolution and a small sample volume to
produce images with two-color directional
information with less ‘blooming’ of color for more
realistic representation of vessel size. It depicts flow
at a lower velocity than does color or power
Doppler, and has the advantage of showing flow
direction. It can be combined with static 3D or 4D
gated acquisition (STIC) and the glass-body mode,
to produce high-resolution images of the vascular
tree with bidirectional color coding (Figure 7).

• This technique is particularly sensitive for imaging
small vessels. High resolution bidirectional power
flow Doppler combines the flow information
provided by color Doppler with the anatomic
acuity associated with power Doppler. Owing to
this modality’s sensitivity systolic and diastolic
flow are observed at the same time, for example,
when used with STIC acquisition the ductus
venosus is shown to remain filled both in systole
and in diastole.

• B-flow
• B-flow is an ‘old-new’ technology that images blood
flow without relying on Doppler shift. B-flow is an
outgrowth of B-mode imaging that, with the advent of
faster frame rates and computer processing, allows the
direct depiction of blood cell reflectors. It avoids some
of the pitfalls of Doppler flow studies, such as aliasing
and signal dropout at orthogonal scanning angles. The
resulting image is a live gray-scale depiction of blood
flow and part of the surrounding lumen, creating
sensitive ‘digital casts’ of blood vessels and cardiac
chambers (Figure 8).

• This also makes B-flow more sensitive for
volume measurement. When applied to 3D
fetal echocardiography B-flow modality is a
direct volume non-gated scanning method
able to show blood flow in the heart and
great vessels in real-time, without color
Doppler flow information

SCREENING EXAMINATION OF
THE
FETAL HEART WITH 3D/4D
ULTRASOUND
• Guidelines for the performance of fetal heart examinations
have been published by the International Society of
Ultrasound in Obstetrics and Gynecology (ISUOG).These
guidelines for ‘basic’ and ‘extended basic’ fetal cardiac
scanning are amenable to 3D/4D applications, and 3D/4D can
enhance both basic and extended basic fetal cardiac scans, as
well as evaluation of congenital anomalies. Many research
teams have applied 3D ultrasound and STIC acquisition to
fetal echocardiography, and various techniques have been put
forward to optimize the use of this modality. A well-executed
STIC acquisition5 contains all the necessary planes for
evaluation of the five classic transverse planes of fetal
echocardiography.

• The operator can examine the fetal upper abdomen
and stomach, then scroll cephalad to obtain the
familiar four chamber view, the five-chamber view,
the bifurcation of the pulmonary arteries, and
finally the three-vessel and trachea view. Slight
adjustment along the x- or y-axis may be necessary
to optimize the images. Performed properly, this
methodology will provide the examiner with all the
necessary planes to conform with the guidelines.
However, it must be remembered that STIC
acquisition that has been degraded by maternal or
fetal movements, including fetal breathing
movements, will contain artifacts within the scan
volume.

POTENTIAL PITFALLS
OF 3D/4D
ECHOCARDIOGRAPHY
• 3D/4D fetal echocardiography scanning
is prone to artifacts similar to those
encountered in 2D ultrasonography, and
some that are specific to 3D/4D
acquisition and post-processing.

STIC acquisition
quality
• The quality of a STIC acquisition may be adversely
affected by fetal body or ‘breathing’ movements;
quality is improved by scanning with the fetus in
a quiet state, and using the shortest scan time
possible. When reviewing a STIC acquisition, the
B-frame will reveal artifacts introduced by fetal
breathing movements (Figure 9). If the B-frame
appears sound, the volume is usually acceptable,
and can be used for further investigation. It must
be stressed again that the quality of the original
acquisition will affect all further stages of post-
processing and evaluation.

ACCURACY
• Several studies have compared imaging yield
between 2D and 3D/4D fetal echocardiography,
others have examined the feasibility of 3D/4D and
STIC in screening programs, while others have
described the application of various 3D/4D
modalities to the diagnosis or evaluation of fetal
cardiovascular anomalies. However, no large study
has examined the contribution of 3D/4D
ultrasonography to the accuracy of fetal
echocardiography screening programs.

• In coming years, studies will direct 3D/4D capabilities to
the evaluation of fetal cardiac functional parameters.
This may provide insights into the physiological effects
of fetal structural or functional cardiac defects, or
maternal diseases such as diabetes, on the developing
fetus. To the best of our knowledge, no large study has
been performed to date to examine whether the
addition of 3D/4D methods to fetal echocardiography
screening programs increases the detection rate of
cardiac defects. This technology has reached the stage
when its reproducibility and added value in screening
accuracy should be tested in large prospective studies,
not only by teams or in centers that have made 3D/4D
their specialty, but among the generality of
professionals performing fetal echocardiography.

REFERENCES
• 1. DeVore GR, Falkensammer P, Sklansky MS, Platt LD. Spatiotemporal
image correlation (STIC): new technology for evaluation of the fetal
heart. Ultrasound Obstet Gynecol 2003;22: 380–387.
• 2. Deng J. Terminology of three-dimensional and four-dimensional
ultrasound imaging of the fetal heart and other moving body
parts.Ultrasound Obstet Gynecol 2003; 22: 336–344.
• 3. Goncalves LF, Lee W, Chaiworapongsa T, Espinoza J,Schoen ML,
Falkensammer P, Treadwell M, Romero R. Fourdimensional
ultrasonography of the fetal heart with spatiotemporal image correlation.
Am J Obstet Gynecol 2003; 189:1792–1802.
• 4. Falkensammer P. Spatio-temporal image correlation for volume
ultrasound. Studies of the fetal heart. GE Healthcare: Zipf, Austria, 2005.
• 5. Goncalves LF, Lee W, Espinoza J, Romero R. Examination of the fetal
heart by four-dimensional (4D) ultrasound with spatiotemporal image
correlation (STIC). Ultrasound Obstet Gynecol 2006; 27: 336–348.

3D – 4D
Ultrasound
in
Obstetrics
and
Gynecology

• Three dimensional (3D) ultrasound (USG) and 4D i.e. real
• time 3D are a natural development of the imaging technology
• and were first demonstrated nearly 15 years ago, but are
• becoming a clinical reality only now. Methods for 3D
• reconstruction of CT and MRI images have achieved an
• advanced state of development. 3D applications in ultrasound
• have lagged behind CT and MRI, because ultrasound data is
• much more difficult to render in 3D. Only in the past few
• years has the computing power of ultrasound equipment
• reached a level adequate enough for the complex signal
• processing tasks needed to render ultrasound data in three
• dimensions. The clinical application of 3D ultrasound is likely
• to advance rapidly, as improved 3D rendering technology
• becomes more widely available

• The advantages of 3D and 4D ultrasound in certain
areas are unequivocal. Most centres already apply
its use in the workup of fetal anomalies involving
the face, limbs,thorax, spine and the central
nervous system. The use of this technology in
applying color doppler, in guiding needles for
different puncture procedures as well in evaluating
• the fetal heart are currently under close research
scrutiny.

• 3D ultrasound helps the bonding between the parents
and their future offspring, and consultants understand
fetal pathology better and can plan postnatal
interventions better. The multiplanar presentation and
niche mode are quite useful to determine the extension –
inside or outside the organs, of nodules, cysts or tumors.
The volume measurement is better assessed with 3D and
we can perform studies that follow growth in order to
decide medical or surgical treatment. The VOCAL(R)
makes it possible to obtain a proper after-treatment
follow-up of focal disorders in these small organs.
Neovascularization is clearly viewed with 3D USG and
probably can suggest malignant origin of a neoplasm. 3D
USG offers a more comprehensive image of anatomical
structures and pathological conditions and also permits
observation of the exact spatial relationships

• More studies are needed to demonstrate
specificity and sensitivity of 3D and 4D USG.
There are limitations to adequate visualization
of fetal anatomy with 3D/4D technology. If
there is inadequate amniotic fluid surrounding
the fetus, or if the fetus has its face in the
posterior position in the uterus, there will be
difficulty visualizing structures and the face.

• 3D allows a simultaneous display of multiple sequential
parallel planes of the fetal structures, but there is some
uncertainty if an isolated image in one of the multislice
images represents the exact level of a fetal structure.
Another problem is the creation of false expectations and
overall the medical value is limited. Pregnant women will
ask for a picture of their fetus like those they have seen in
advertisements and put pressure on the scanning centres.
Such is the demand in the United States that technician
operated 4D ultrasounds are readily available in scanning
booths in shopping malls, enabling parents to purchase a
video of their moving fetus. This creates problems later on
when women, having already had such USG, do not realise
that they need a targeted anomaly scan

• Endometrial thickness, endometrial pattern, pulsatility
index (PI) and resistance index (RI) of uterine vessels,
endometrial volume, vascularization index (VI), flow
index (FI) and vascularization flow index (VFI) of
endometrial and subendometrial regions have been
studied by 3D with power dopplers on the day of oocyte
retrieval in patients undergoing the first IVF cycle.
Uterine RI, endometrial VI and VFI were significantly
lower in the pregnant group than in the nonpregnant
group. There was a nonsignificant trend of higher
implantation and pregnancy rates in patients with absent
endometrial or subendometrial blood flow. The number of
embryos replaced and endometrial VI were the only two
predictive factors for pregnancy.

• Endometrial and subendometrial
blood flows measured by 3D power
Doppler ultrasound were not good
predictors of pregnancy if they were
measured at one time-point during
IVF treatment. A similar study noted
that endometrial volume decreased
significantly after hCG injection in
women who conceived, but not in
those who did not.

• Along with crown-rump length (CRL), the size
(diameter) of embryonic structures such as
gestational sac (GS) and yolk sac (YS) may have
prognostic value for embryonic development. First
trimester volume calculations of these structures
using transvaginal 3D USG technic have been done.
Volumetry of GS proved to be a sensitive predictor
for pregnancy outcome and can be a good
supplement to CRL measurements. However, no
statistically significant difference was found when YS
volumes of normal and abnormal pregnancies were
compared. Specificity, sensitivity, positive and
negative predictive values of GS volumes and CRL
were similar. Mean YS/GS ratios also had good
predictive values (P <0.05)

• 4D was successfully used to perform amniocentesis,
CVS,cordocentesis, and intrauterine transfusion.
Using 4D USG guidance, most procedures were
performed within 5 minutes and with a 100% success
rate, even in cases involving severe oligohydramnios,
thin placenta and narrow umbilical veins. Moreover,
there were no serious complications during or after
any procedure. This appeared to contribute to the
accuracy of needle placement by eliminating the
lateralization phenomenon when a fixed needle
guide attachment was used.
• Needle tip visualization was seen in each orthogonal
plane inmost freehand 4D amniocentesis cases

• Presently, both 2D and 4D methods are required for the
assessment of early fetal motor development and motor
behavior. Several movement patterns, such as sideway
bending, hiccup, breathing movements, mouth opening
and facial movements could be observed only by 2D USG
.Isolated hand movement and subtypes of hand
movements were easily recognized by 4D USG.
• All subtypes of hand to head movement can be seen from
13 weeks of gestation with fluctuating incidence. Facial
activities and different forms of expression are easily
recognized. 4D USG is superior over real time 2D USG for
qualitative, but inferior for quantitative analysis of hand
movements. 4D USG makes it possible to determine the
exact direction of the fetal hand, but the exact number of
each type of hand movements can still not be
determined.4D USG is superior to 2D USG in the
evaluation of complex facial activity and expression.

Among facial activities observed by 4D USG,
simultaneous eyelid and mouth movements
dominate between 30 and 33 weeks of gestation.
Pure mouth movements such as mouth opening,
tongue expulsion, yawning and pouting are
present, but at a significantly lower incidence.
Facial expressions such as smiling and scowling can
be precisely observed using 4DUSG 12. There were
no movements observed in fetal life that were not
present in neonatal life; the Moro reflex was
present only in neonates

• Inclusion of 3D and 4D ultrasound imaging in the
examination of cleft lip and/or palate, allows
easier and more rapid screening and more precise
evaluation of the different cleft constituents . 3D
USG can be a reliable technic for visualizing most
fetal cranial sutures and fontanels. By performing
a sagittal and a transverse scan, most of the
sutures and fontanels can be made visible during
the second half of pregnancy. Visualization
depends on gestational age Gray-scale and color
Doppler dynamic 3D displays and multiplanar
views used to assess cardiac gating and cardiac
morphology demonstrate clinically useful 4D
images of the fetal heart. The reconstruction of 3D
and multiplanar views provided additional views
not obtainable by 2D imaging

• Approximately one third of clinical
rectoceles do not show a sonographic
defect, and the presence of a defect is
associated with age, not parity . While 3D
pelvic floor imaging is a field that is still in
its infancy, it is already clear that the
method has opened up entirely new
opportunities for the observation of
functional anatomy.

• The exact applicability of 3D and 4D USG is
yet to be ascertained. The American
Institute of Ultrasound in Medicine has
convened a panel of physicians and
scientists with interest and expertise in 3D
USG to discuss the current diagnostic
benefits and technical limitations in
obstetrics and gynecology and to consider
the utility and role of this type of imaging in
clinical practice now and in the future

References
• 1. Lees W. Ultrasound imaging in three and four dimensions. Seminars
in Ultrasound, CT & MR. 2001;22:85-105.
• 2. Timor-Tritsch IE, Han E, Platt LD. Three-dimensional ultrasound
experience in obstetrics. Curr Opin Obstet Gynecol 2002;14:569-75.
• 3. Maymon R, Herman A. Ariely S et al. Three-dimensional vaginal
sonography in obstetrics and gynaecology. Hum Reprod Update2000;
6:475-84.
• 4. Fernandez LJ, Aguilar A, Pardi S. Three-dimensional ultrasound in
small parts: Is it just a nice picture? Ultrasound Quarterly2004;20:119-
25.
• 5. Leung KY, Ngai CSW, Chan BC et al. Three-dimensional extended
imaging: a new display modality for three-dimensional ultrasound
examination. Ultrasound Obstet Gynecol. 2005; 26:244-51.
• 6. Ng EHY, Chan CCW, Tang OS et al. The role of endometrial and sub
endometrial blood flows measured by three-dimensional power
Doppler ultrasound in the prediction of pregnancy during IVF
treatment. Hum Reprod 2006; 21:164-70.

Determination
of Gestational
Age
by Ultrasound

To assist clinicians in assigning gestational age based on
ultrasound biometry.
• To determine whether ultrasound dating provides
more accurate gestational age assessment than
menstrual dating with or without the use of
ultrasound.
• To provide maternity health careproviders and
researchers with evidence-based guidelines for the
assignment of gestational age.
• To determine which ultrasound biometric parameters
are superior when gestational age is uncertain.
• To determine whether ultrasound gestational age
assessment is cost effective.

• Accurate assignment of gestational age may reduce
post-dates labour induction and may improve
obstetric care through allowing the optimal timing of
necessary interventions and the avoidance of
unnecessary ones. More accurate dating allows for
optimal performance of prenatal screening tests for
aneuploidy. A national algorithm for the assignment
of gestational age may reduce practice variations
across Canada for clinicians and researchers.
Potential harms include the possible reassignment of
dates when significant fetal pathology (such as fetal
growth restriction or macrosomia) result in a
discrepancy between ultrasound biometric and
clinical gestational age. Such reassignment may lead
to the omission of appropriate—or the performance
of inappropriate—fetal interventions.

• 1. When performed with quality and
precision, ultrasound alone is more accurate
than a “certain” menstrual date for
determining gestational age in the first and
second trimesters (≤ 23 weeks) in
spontaneous conceptions, and it is the best
method for estimating the delivery date.
• 2. In the absence of better assessment of
gestational age, routine ultrasound in the
first or second trimester reduces inductions
for post-term pregnancies.

• 3. Ideally, every pregnant woman should be
offered a first-trimester dating ultrasound;
however, if the availability of obstetrical
ultrasound is limited, it is reasonable to use a
second-trimester scan to assess gestational
age.
• 4. Notwithstanding Summary Statements 1, 2,
and 3, women vary greatly in their awareness
of their internal functions, including ovulation,
and this self-knowledge can sometimes be very
accurate.

• The accurate dating of pregnancy is critically important for
pregnancy management from the first trimester to
delivery, and is particularly necessary for determining
viability in premature labour and in post-dates
deliveries.Prior to the widespread use of ultrasound,
caregivers relied on a combination of history and physical
examination to clinically determine gestational age.
Ultrasound gave clinicians a method to measure the fetus
and therefore to estimate gestational age. Much of our
current clinical practice is based on studies from the 1980s
and 1990s. As new information emerges in fields, such as
reproductive biology, perinatal epidemiology, and medical
imaging, our current clinical practice is being challenged.
“Certain” menstrual dating, for example, is less certain
than previously thought.

• When ultrasound is performed with
quality and precision, there is
evidence to suggest that dating a
pregnancy using ultrasound
measurements is clinically superior to
using menstrual dating with or
without ultrasound, and this has been
advocated and adopted in other
jurisdictions.

• 1. First-trimester crown-rump length is the
best parameter for determining gestational
age and should be used whenever appropriate.
• 2. If there is more than one first-trimester scan
with a mean sac diameter or crown-rump
length measurement, the earliest ultrasound
with a crown-rump length equivalent to at
least 7 weeks (or 10 mm) should be used to
determine the gestational age.
Recommendations

• 3. Between the 12th and 14th weeks, crown-rump
length and biparietal diameter are similar in
accuracy. It is recommended that crown-rump
length be used up to 84 mm, and the biparietal
diameter be used for measurements > 84 mm.
• 4. Although transvaginal ultrasound may better
visualize early embryonic structures than a
transabdominal approach, it is not more accurate in
determining gestational age. Crown-rump length
measurement from either transabdominal or
transvaginal ultrasound may be used to determine
gestational age.

• 5. If a second- or third-trimester scan is used
to determine gestational age, a combination of
multiple biometric parameters(biparietal
diameter, head circumference, abdominal
circumference, and femur length) should be
used to determine gestational age, rather than
a single parameter.
• 6. When the assignment of gestational age is
based on a third trimester ultrasound, it is
difficult to confirm an accurate due date.
Follow-up of interval growth is suggested 2 to
3 weeks following the ultrasound.

GESTATIONAL AGE ESTIMATES
USING CLINICAL DATING
• The clinical estimate of gestational age typically
relies on clinical history (menstrual cycle length,
regularity, and recall of the first day of the last
menstrual period), followed by confirmation by
physical examination or other signs and
symptoms.

Dating Based on Menstrual History
• Dating by certain menstrual history is inexpensive and
• readily available. Typically, the EDD is based on a 280-
• day gestation from the first day of the LMP. Certain
• menstrual dating criteria assume regular cycles,
ovulation
• at the midpoint of the cycle, fertilization on the middle
• day of the cycle, correct recall of the onset of the LMP,
• and the woman having been free of oral contraceptives
• for several months prior.

• Women vary greatly in their
• awareness of their internal functions, including ovulation.
• Their self-knowledge of ovulation can sometimes be very
• accurate; however, the only truly certain clinical history
• is one in which the dates of ovulation, fertilization,
• and implantation are precisely known, as in ART, in
• which records include the date of oocyte retrieval, and
• other methods of timed ovulation and fertilization.
• Unfortunately, without timed ovulation and fertilization
• as in ART and other timed methods, clinical history is
• often not reliable.10 Campbell et al. demonstrated that
• 45% of pregnant women are uncertain of menstrual
• dates as a result of poor recall, irregular cycles, bleeding
• in early pregnancy, or oral contraceptive use within 2
• months of conception

• Even if menstrual history is correct, the exact time
• of ovulation, fertilization, and implantation cannot be
• known. Women may undergo several “waves” of follicular
• development during a normal menstrual cycle, which
• may mean ovulatory inconsistency during any given
• cycle.12,13 Sperm may survive for 5 to 7 days in the female
• reproductive tract, a “known” conception date is therefore
• not completely reliable.14 Recent studies suggest the
• ovulation-to-implantation duration can vary by as much as
• 11 days, and this may affect fetal size and growth.15 Even
• in women who are certain of menstrual dating, delayed
• ovulation is an important cause of perceived prolonged
• pregnancy and is more likely to occur than early ovulation.16
• Some authors have suggested that 282 days should be used
• instead of 280 to improve dating accuracy, since it is more
• likely that women will ovulate later rather than earlier than
• predicted.9 All of these factors conspire to make it difficult
• to accurately predict gestational age based on menstrual
• history.

Dating Based on Clinical Examination
• The size of the uterus, estimated through pelvic or
• abdominal examination, can be roughly correlated with
• gestational age; however, factors that affect uterine size
• (such as fibroids) and maternal body characteristics (such
• as obesity) will affect such an estimate. The uterus is
• approximately the size of a grapefruit at 10 to 12 weeks.
• At 20 weeks the fundus reaches the umbilicus. After 20
• weeks the symphysis fundal height, in centimetres, should
• correlate with the week of gestation.7,17 Fetal heart tones
• are audible at 11 to 12 weeks with electronic Doppler
• devices, and this audibility can also assist in the clinical
• assignment of gestational age.

Gestational Age
Estimation Based
on Ultrasound
Findings

• Ultrasound biometric measurements determine
• gestational age based on the assumption that the size of
• the embryo or fetus is consistent with its age. Biological
• variation in size is less during the first trimester than in
• the third trimester. Ultrasound estimation of gestational
• age in the first trimester is therefore more accurate than
• later in pregnancy.18 Full descriptions of each parameter
• and published ranges of accuracy are outlined in Table 2.

• The determination of gestational age in the first trimester
• uses the mean gestational sac diameter and/or the crown–
• rump length. During the first 3 to 5 menstrual weeks an
• intrauterine pregnancy is first signaled by the presence
• of a gestational sac.19 The gestational sac represents the
• chorionic cavity, and its echogenic rim represents the
• implanting chorionic villi and associated decidual tissue.20
• The smallest gestational sac size that can be clearly
• distinguished by high frequency transvaginal transducers
• is 2 to 3 mm, which corresponds to a gestational age of
• about 32 to 33 days.21 The MSD is a commonly used,
• standardized, way to estimate gestational age during early
• pregnancy. It is less reliable when the MSD exceeds 14 mm
• or when the embryo can be identified.22 The growth of
• the MSD is approximately 1 mm per day.23 CRL has lower
• interobservor variability than MSD, and may thus be better
• for dating a pregnancy

• Yolk Sac
• When the yolk sac appears in the gestational sac it provides
• confirmation of an intrauterine pregnancy and may be
• initially visible as early as the start of the 5th week or as
• late as the 6th week. It grows to a maximal size of 6 mm
• by 10 weeks and gradually migrates to the periphery of
• the chorionic cavity. At the end of the first trimester it
• becomes undetectable. Although the presence of the yolk
• sac is helpful in determining the presence of an intrauterine
• pregnancy, direct measurement of this structure is not
• useful in determining gestational age

• Crown-Rump Length
• Direct measurement of the CRL provides the most
• accurate estimate of gestational age once the embryo is
• clearly seen. Ideally, either the best CRL or the average
• of several satisfactory measurements should be used.26
• The CRL measurement is reported to be accurate for
• dating to within 3 to 8 days.22,27–39 The MSD should not
• be used to estimate gestational age once the CRL can be
• measured

• The narrowest confidence interval appears to be
• between 7 and 60 mm for CRL.3,29,30,40 The slope of the
• embryonic growth curve is small before this time and it
• can be difficult to clearly identify a very early fetus; thus,
• it is this committee’s expert opinion that reliability and
• measurability is best when the CRL is at least 10 mm. If
• more than one scan is performed in the first trimester, the
• earliest scan with a CRL of at least 10 mm should be used.
• To avoid performing extra ultrasounds, it is acceptable to
• time the dating scan to coincide with nuchal translucency
• screening (if available).
• Several studies have evaluated CRL and BPD between
• 12 and 14 weeks, with conflicting results. The majority
• suggest there is no clinically important difference among
• confidence intervals, suggesting that either CRL or BPD
• should be used at this gestational age.41–44 The 84 mm
• threshold for CRL for estimating gestational age, as
• suggested by the ISUOG, seems reasonable

• Recommendations
• 1. First-trimester crown-rump length is the
• best parameter for determining gestational
• age and should be used whenever
• appropriate. (I-A)
• 2. If there is more than one first-trimester scan
• with a mean sac diameter or crown-rump length
• measurement, the earliest ultrasound with a crownrump
• length equivalent to at least 7 weeks (or
• 10 mm) should be used to determine the gestational
• age.

• 3. Between the 12th and 14th weeks, crown-
rump
• length and biparietal diameter are similar in
accuracy.
• It is recommended that crown-rump length be
used
• up to 84 mm, and the biparietal diameter be
used for
• measurements > 84 mm.

• Recommendation
• 4. Although transvaginal ultrasound may better
• visualize early embryonic structures than a
• transabdominal approach, it is not more accurate
• in determining gestational age. Crown-rump
length
• measurement from either transabdominal or
• transvaginal ultrasound may be used to
determine
• gestational age.

Transabdominal Versus
Transvaginal Ultrasonography
• Transvaginal ultrasound is typically used to evaluate
• early first trimester pregnancy structures, such as the
• gestational sac, yolk sac, and embryo. Original studies
• comparing transabdominal and transvaginal techniques in
• early pregnancy demonstrated that TV was the superior
• method.45–47 Perhaps because of better technology, more
• recent studies have not found the same result. Grisolia
• et al. concluded that the accuracy of TV ultrasound
• has not been shown to be superior to TA ultrasound in
• dating pregnancies.31 Other authors have found that TA is
• comparable to TV in determining gestational age if CRL is
• measurable after 6 weeks.

• Crown-Rump Length in Pregnancies Conceived
• by Assisted Reproductive Technology
• When the conception date is known absolutely, as with
• timed ovulation/fertilization during ART, the EDD
• should be calculated based on the fertilization date.
• Studies have demonstrated that the CRL
measurements
• in IVF pregnancies are those to be expected in naturally
• conceived pregnancies, suggesting that study results
can be
• extrapolated between the 2 populations

Signs of Fetal Maturity
• Identification of certain US findings suggest that a fetus
• has reached the third trimester and may correlate with
• fetal lung maturity and gestational age. These parameters
• are the epiphyseal ossification centres of the distal femur,
• proximal tibia, and proximal humerus. The measurement of
• these ossification centres does not precisely correlate with
• gestational age; however, their presence may be helpful late
• in pregnancy when the gestational age is not known. The
• presence of distal femoral epiphysis has a PPV of 96% for
• indicating a pregnancy of at least 32 weeks, the proximal
• tibial epiphysis has a PPV of 83% for indicating a pregnancy
• of at least 37 weeks, and the proximal humeral epiphysis
• has a PPV of 100% for indicating a pregnancy of at least
• 38 weeks

WHAT IS THE BEST METHOD
FOR ASSIGNING GESTATIONAL AGE?
• Currently, most centres in Canada use a combined
• approach in which US is used to confirm reliable
• menstrual dating. If there is an unreliable menstrual
• history, the US prediction of EDD is used. Clinical
• judgement is used to resolve conflicting data. However,
• centres vary in terms of confidence intervals and
• biometry charts used.
• Many studies evaluating menstrual dating, compared with
• US dating, in the first and second trimesters have found US
• dating superior for predicting the actual date of delivery.92–98
• No study has shown that it is inferior to menstrual dating.
• Menstrual dating underestimates the US-based EDD by
• an average of 2 to 3 days.95 Ultrasound dating alone was
• significantly better in predicting the actual date of delivery
• than any of the dating policies using menstrual dates alone
• or in combination with US

• Many studies document that the use of US dates reduces
• the rate of post-dates pregnancy by about 70% even in
• the face of certain menstrual history.92,96,97,99,100 The
most
• recent Cochrane systematic review found reduced rates
• of induction for post-term pregnancy (OR 0.59; 95% CI
• 0.42 to 0.83) among women who underwent routine US
• in early pregnancy (< 24 weeks) and concluded that early
• pregnancy US enables better gestational age assessment,
as
• well as conferring other benefits

• Using US-based gestational age assignment would also
• result in improved performance of prenatal screening
• programs. Using US estimates exclusively would increase
• sensitivity for Down syndrome anywhere from 9% to 16%,
• and/or decrease false-positive rates (for a set sensitivity)
• by 2.6%.102,103 There might be a very slight increase in the
• screening positive rate for open neural tube defects, but
• this is more than offset by the decrease in false-positive
• rates for Down syndrome. The common practice of
• using certain menstrual dates confirmed by US is inferior
• to using US alone.104 In the context of serum screening,
• first and early second-trimester US parameters perform
• similarly.

Important notes
• 1. When performed with quality and precision,
• ultrasound alone is more accurate than a “certain”
• menstrual date for determining gestational age
• in the first and second trimesters (≤ 23 weeks) in
• spontaneous conceptions, and it is the best method
• for estimating the delivery date. (II)
• 2. In the absence of better assessment of gestational
• age, routine ultrasound in the first or second
• trimester reduces inductions for post-term
• pregnancies

• 3. Ideally, every pregnant woman should be offered
• a first trimester dating ultrasound; however, if the
• availability of obstetrical ultrasound is limited, it is
• reasonable to use a second trimester scan to assess
• gestational age. (I)
• 4. Notwithstanding Summary Statements 1, 2, and
• 3, women vary greatly in their awareness of their
• internal functions, including ovulation, and this
selfknowledge
• can sometimes be very accurate.

SHOULD ROUTINE FIRST
TRIMESTER
DATING ULTRASOUNDS BE
OFFERED TO ALL
PREGNANT WOMEN?

• A routine first trimester US has many advantages: early
• identification of gross anomalies and multiple gestations,
• more precise dating, improved performance of prenatal
• screening, and an opportunity to perform nuchal
• translucency as part of prenatal genetic screening. In many
• jurisdictions, a dating US is performed routinely in all
• women, regardless of menstrual history. The availability,
• quality, and health care cost of obstetrical US is a significant
• factor in local patterns of practice.2 Crowther et al. found
• routine early US (< 17 weeks) provided more precise
• estimates of gestational age than later US (18 to 22 weeks),
• reduced the need to adjust the EDD in mid-gestation, and
• decreased maternal anxiety

• The balance of the literature supports using first trimester
• US to reduce the incidence of induction for post-dates
• pregnancy. Although no comprehensive cost
• benefit analysis has been done on routine early US for
• dating, the current literature suggests significant benefits
• are present. Ideally, where it is readily available, a first
• trimester US for dating should be performed. Where
• nuchal translucency is available, this scan can serve both
• functions. When a first trimester US cannot be obtained,
• the available evidence suggests the second trimester US
• can be used for similar benefits

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