In Vitro Fertilization (IVF)
IVF refers to conception that occurs in a laboratory versus fertilization that occurs in the fallopian tube (in vivo). The first human IVF pregnancy followed retrieval of a single oocyte in a spontaneous menstrual cycle and transfer of the embryo during the luteal phase. However, the inefficiency of LH monitoring, aspiration of a single follicle and transferring a single embryo led to disappointing pregnancy rates. Currently, most ART programs employ controlled ovarian hyperstimulation in an effort to maximize pregnancy rates. Ovulation induction for IVF can be classified into:
- Routine IVF with pituitary down-regulation with gonadotropin-releasing hormone (GnRH) agonist
- Poor response protocols
- Natural cycle IVF
Routine IVF
GnRH-agonist down-regulation. GnRH-agonist (eg. Lupron) is administered to down-regulate pituitary gonadotropin production to allow ovarian stimulation in a controlled. Prior to the use of GnRH agonists, cycle cancellation rates approached 30 percent due to premature follicular luteinization caused by spontaneous LH surges. GnRH-agonists have decreased the cycle cancellation rate from 50 percent to < 10 percent.
Long protocol. GnRH agonists are administered in a "long" or "short" protocol. The preferred method of GnRH agonist administration is the long protocol in which pituitary suppression is initiated during the luteal phase of the prior cycle (day 21). After 10-14 days of GnRH agonist down-regulation is achieved and gonadotropin therapy is initiated. GnRH agonist is continued until the administration of human chorionic gonadotropin (hCG) when follicular size is >18mm.
Short protocol. GnRH-agonist may be initiated in the follicular phase (day 2) allowing for ovarian stimulation from endogenous gonadotropins followed by exogenous gonadotropin administration. This short protocol or flare protocol is typically reserved for patients who are poor responders to exogenous gonadotropins.
After down-regulation with GnRH, ovulation induction is initiated with exogenous gonadotropins. Currently available gonadotropin preparations include human menopausal gonadotropins (HMG), formulated in ampules containing 75 IU each of FSH and LH; purified FSH, which contains 75 IU of FSH with less than 1 IU of LH; and recombinant FSH with > 99 percent purity. The majority of patients will require at least 10 days of gonadotropin stimulation until follicular maturity is reached based on sonographic measurements and serum estradiol levels.
When the mean diameter of the lead follicles are 18mm 5,000-10,000 IU of hCG is administered. Administration of hCG is crucial as premature hCG injection may lead to the recovery of predominantly immature oocytes and delayed injection will yield postmature oocytes. Retrieval of oocytes is performed between 34-38 hours after the administration of hCG. Mature oocytes are insemination with washed sperm approximately 4-6 hours following retrieval. Fertilization can be determined 16-18 hours after insemination and zygotes are continued to grow in special culture media. At 48 hours post-retrieval, 90 percent of the zygotes will have cleaved and are at the 4- to 6-cell stage. At 72 hours, healthy embryos are at the 6- to 10-cell stage. Prior to 1998, embryo transfers have normally occurred between 48 and 72 hours, however, improvement in culture conditions have allowed embryos to be cultured to blastocyst (120 hours) with improvement in pregnancy rates and a reduction in the multiple gestation rate. Intramuscular progesterone is used for support during the luteal phase. A serum bhCG is obtained 9 days following blastocyst transfer.
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Poor Response Protocols
Poor ovarian response to stimulation occurs in 9-24 percent of patients. Poor responders are patients with peak estradiol levels < 500pg/ml, < 4 dominant follicles on day of hCG, patients >40 years of age and those with diminished ovarian reserve based on day 3 FSH. Several stimulation protocols have been proposed in an attempt to improve ovarian stimulation. These include: 1) initiating GnRH agonist and gonadotropins together in the follicular phase (flare protocol), 2) co-treatment with estrogen, growth hormone or oral contraceptives or 3) using clomiphene citrate plus gonadotropins without GnRH agonist down-regulation. Currently, most centers are using microflare protocols in which patients are pretreated with a monophasic OC for approximately 6 weeks followed by 20ug leuprolide acetate twice daily (versus 1 mg daily in conventional IVF) and 6 ampules of gonadotropins 3 days later. Studies have shown that patients respond with higher peak estradiol levels, an increase in the number of follicles and an increase in the number of oocytes retrieved.
Natural cycle
The ultimate minimal stimulation protocol is natural cycle IVF that uses no form of exogenous stimulation. Pregnancy rates are only 10-12 percent per oocyte retrieval, and thus natural cycle IVF is rarely performed.
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