1. 個體化促超排卵方案
Dr. Milton Leong
MDCM DSc (McGill)
Director, IVF Center, HKSH
Specialist in Reproductive Medicine
Adjunct Professor, OBS-GYN, McGill University
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Porter RN, Smith W., Craft IL., Abdulwahid NA., JAcobs HS (1984) Induction of ovulation for in-vitro fertilization using buserelin and gonadotropins. Lancet 2; 1284-1285
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Modification of position 6 and 10 is typical for all GnRH agonists. This leads to a change in
-GnRH receptor affinity (which is increased)
-regulation of biologic activity (which is increased due to a longer half life)
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Action of GnRH agonists
1. Binding of GnRH leads to a post-receptor-cascade and this consecuitively to the release of LH and FSH
2. Adding of GnRH agonists will lead - because they have a higher affinitiy to the receptors and have a higher biologic potency - to binding of the agonists to the receptors instead of the natural GnRH.
3. Initially, this will lead to an increase in the receptor action, number and post-receptor-cascade with a consecutive increase in the release of LH and FSH (flare up effect).
4. After that, however, receptors are internalized, lysed, the number of receptors decreases, the post-receptor-cascade is downregulated and the stimulus to release LH and FSH will also be suppressed.
5. Downregulation and pituitary suppression will result.
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In the long luteal protocol a GnRH agonist depot preparation is administered during the mid-luteal phase of the preceeding cycle, or a GnRH agonist is started with a daily administration at that time.
Two weeks later, in between menstruation will start, pituitary suppression is achieved. At that time point a transvaginal ultrasound should be done to exclude cyst formation, since the flare up effect of the agonist may lead to ovarian cyst formation. If pituitary suppression has been achieved and the ovaries do not show cysts, gonadotropin stimulation can be started at that day. It will go on until hCG can be administered for ovulation induction.
Luteal phase support is necessay for these protocols.
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In contrast to GnRH agonists, there are more changes necessary in the structure of the natural GnRH molecule, to achieve antagonistic properties. These antagonistic properties mean:
- no intrinsic effect
- competitive action
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Action of GnRH antagonists
1. Binding of GnRH leads to a post-receptor-cascade and this consecutively to the release of LH and FSH
2. Adding of GnRH antagonists will lead to a competitive action of GnRH and GnRH antagonists - which do not have any intrinsic activity.
3. A sudden downregulation of the post-receptor-cascade is the result with a consecutive decrease in the stimulus to release LH and FSH.
4. Pituitary suppression is achieved within a few hours without any initial flare up effect.
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In the multiple dose antagonist protocol ovarian stimulation is started with the second or third day of the menstrual cycle.
Cetrotide® 0.25 mg is started on the 6th day of ovarian stimulation in the morning or on the 5th day in the evening. And is administered up to and including the day of hCG, if given in the morning.
