In vitro fertilization procedure
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Procedure
Ovarian Stimulation
Treatment cycles are typically started on the third day of menstruation and consist of a regimen of fertility medications to stimulate the development of multiple follicles of the ovaries. In most patients injectable gonadotropins (usually FSH analogues) are used under close monitoring. Such monitoring frequently checks the estradiol level and, by means of gynecologic ultrasonography, follicular growth. Typically approximately 10 days of injections will be necessary. Spontanenous ovulation during the cycle is prevented by the use of GnRH agonists or GnRH antagonists, which block the natural surge of luteinizing hormone (LH).
Oocyte Retrieval
When follicular maturation is judged to be adequate, human chorionic gonadotropin (β-hCG) is given. This agent, which acts as an analogue of luteinizing hormone, would cause ovulation about 36 hours after injection, but a retrieval procedure takes place just prior to that, in order to recover the egg cells from the ovary. The eggs are retrieved from the patient using a transvaginal technique involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries. Through this needle follicles can be aspirated, and the follicular fluid is handed to the IVF laboratory to identify ova. The retrieval procedure takes about 20 minutes and is usually done under conscious sedation or general anesthesia.
Fertilization
In the laboratory, the identified eggs are stripped of surrounding cells and prepared for fertilisation. In the meantime, semen is prepared for fertilization by removing inactive cells and seminal fluid. The sperm and the egg are incubated together (at a ratio of about 75,000:1) in the culture media for about 18 hours. By that time fertilization should have taken place and the fertilised egg would show two pronuclei. In situations where the sperm count is low, a single sperm is injected directly into the egg using intracytoplasmic sperm injection (ICSI). The fertilised egg is passed to a special growth medium and left for about 48 hours until the egg has reached the 6-8 cell stage.
Selection
Laboratories have developed grading methods to judge oocyte and embryo quality. Typically, embryos that have reached the 6-8 cell stage are transferred three days after retrieval. In many American and Australian programmes, however, embryos are placed into an extended culture system with a transfer done at the blastocyst stage, especially if many good-quality day-3 embryos are available. Blastocyst stage transfers have been shown to result in higher pregnancy rates.[1]. In Europe, day-2 transfers are common.
Embryo Transfer
Embryos are graded by the embryologist based on the number of cells, evenness of growth and degree of fragmentation. The number to be transferred depends on the number available, the age of the woman and other health and diagnostic factors. In countries such as the UK, Australia and New Zealand, a maximum of two embryos are transferred except in unusual circumstances. For instance, a woman over 35 may have up to three embryos transferred. This is to limit the number of multiple pregnancies. The embryos judged to be the "best" are transferred to the patient's uterus through a thin, plastic catheter, which goes through her vagina and cervix. Several embryos may be passed into the uterus to improve chances of implantation and pregnancy.
Post Transfer
The patient has to wait two weeks before she returns to the clinic for the pregnancy test. During this time she may receive progesterone—a hormone that keeps the uterus lining thickened and suitable for implantation. Many IVF programmes provide additional medications as part of their protocol.
References
- ↑ Papanikolaou EG, Camus M, Kolibianakis EM, Van Landuyt L, Van Steirteghem A, Devroey P (2006). "In Vitro Fertilization with Single Blastocyst-Stage versus Single Cleavage-Stage Embryos". N Engl J Med. 354: 1139. PMID 16540614.