Prenatal diagnosis refers to procedures used to diagnose genetic abnormalities and structural anomalies in early embryos and fetuses. This allows for timely parental counseling and interventions. Common methods of prenatal diagnosis discussed in the document include chorionic villus sampling, amniocentesis, routine ultrasonography, in vitro fertilization, and percutaneous umbilical blood sampling. These methods can diagnose genetic conditions like trisomies as well as structural anomalies. Following an abnormal prenatal test, genetic counselors consider factors like survival and treatment options to counsel parents on continuing or terminating the pregnancy.

1. Prenatal Diagnosis
Asheber Gaym M.D.
January 2009

2. Outline
• Definition of prenatal diagnosis
• Indications of prenatal diagnosis
• Methods of prenatal diagnosis
• Interventions following prenatal diagnosis
2Asheber Gaym,2009

3. Definition of prenatal diagnosis
• Prenatal diagnosis refers to procedures undertaken to
diagnose genetic abnormalities and structural anomalies
of the early embryo and fetus in order to undertake
timely parental counseling and appropriate interventions
• Prenatal diagnostic techniques allow early diagnosis of
fatal genetic and structural anomalies for timely
termination of pregnancy thereby preventing pregnancy
wastage and perinatal mortality
• Prenatal diagnostic techniques require the concerted
efforts of the obstetrician, geneticist and genetic
counselor to reach to the correct diagnosis and
intervention
3Asheber Gaym,2009

4. Indications for prenatal diagnosis
• Maternal age greater than 35
• Past history of delivery of a malformed fetus
• Past history of delivery of a genetically
abnormal fetus
• Family history of genetic diseases
• History of genetic disease in either parent
• Exposure to potential teratogens early in
pregnancy
4Asheber Gaym,2009

5. Methods of Prenatal Diagnosis
Methods Procedure Advantages and Risks
Chorionic
villous
sampling
Transcervical or tranabdominal aspiration
of trophoblastic tissue for karyotyping and
genetic studies in pregnancies less than
nine weeks
Early diagnosis and timely
termination of pregnancy.
3% abortion risk.
Genetic
amniocente
sis
Aspiration of amniotic fluid under
ultrasound guidance and culture and
karyotyping of amniotic cells. Early - < 11
weeks; Late – 16-18 weeks
Early diagnosis and timely
termination of pregnancy.
3% abortion risk. RH
Isoimmunization.
Routine
ultrasonogr
aphy
Performed at 16-18 weeks or earlier to
diagnose structural anomalies of the early
embryo-fetus
Allows second trimester
termination of pregnancy
In vitro
fertilization
Cell taken from the earliest morula for
karyotyping
Allows termination of the
implantation if abnormal
Percultane
ous
umbilical
blood
sampling
PUBS refers to transabdominal aspiration
of fetal blood from the umbilical vein for
detailed analysis of fetal diseases by
performing hematological, genetic,
immunological etc fetal diseases
Allows the diagnosis of
numerous fetal diseases
5Asheber Gaym,2009

6. Methods of Prenatal Diagnosis
Method Procedure Advantages and Risks
Fetoscopy Detailed inspection of fetal
anatomic structures and biopsy
through a fiberoptic device
inserted into the uterus through
the abdominal wall
Risk of abortion is very
high. This procedure has
been superseded by the
less invasive methods such
as CVS and amniocentesis.
Examples of genetic anomalies diagnosed by prenatal diagnosis include trisomies
13,18,21; monosomy X ( Turner’s syndrome); Klienfelter’s syndrome; phenylketonuria;
Gauscher’s disease … etc
Examples of structural anomalies diagnosed by prenatal diagnosis include
anencephaly, hydrocephalus, encepalocele, phecomelia, gastroschissis … etc
6Asheber Gaym,2009

7. Management of abnormal prenatal tests
• Factors important in the decision include:
– Survival chance of the fetus with the identified genetic
or structural abnormality
– Available treatment options if any
– Expected life expectancy with the abnormality
• With the above information, detailed counseling
with both parents is conducted
• Final decision is reached by the parents and
either continuation of pregnancy or termination
of pregnancy is undertaken
7Asheber Gaym,2009