In Vitro Fertilization

Procedure

The first step in the in vitro fertilization process involves the superovulation of the female. In current paradigms, this entails the down—regulation of gonadotrophic—releasing hormone from the hypothalamus which suppresses the anterior pituitary from secreting the gonadotrophins: follicle stimulating hormone and luteinizing hormone. This results in a temporary state of hypogonadotrophic hypogonadism. Once this state is reached, gonad—otrophin stimulation can begin by the administration of follicle stimulating hormone to induce follicle growth in the ovaries. During this time, follicle growth is monitored via ultrasound and by peripheral blood levels of estradiol.

Once follicle size and estradiol levels have reached the desirable size and levels, respectively, human chorionic gonadotrophin is given for ovulation induction. Ovulation in normal cycles is preceded by a surge in luteinizing hormone. Since the β-subunit of human chorionic gonadotrophin is similar to that of luteinizing hormone, human chorionic gonadotrophin is often used in lieu of luteinizing hormone. Once ovulation has been induced, oocyte collection is scheduled to occur within 36 hours postinjection. This 36-hour window is critical because during this time, the oocytes within the follicles will reinitiate meiosis II and will progress to metaphase II.

During oocyte collection, semen will be obtained by masturbation and will be processed typically by gradient centrifugation to remove the seminal plasma and debris. Next, the oocytes and sperm will be combined in a Petri dish to undergo fertilization. An alternative approach is to perform intracytoplasmic sperm injection where an isolated sperm cell is injected into each oocyte. This helps the sperm bypass the zona pellucida of the oocyte and results in high rates of fertilization. Successful fertilization is evidenced by the appearance of two pronuclei in the oocyte at approximately 16–18 hours postinsemination. The pronuclei are said to come into syngamy where the nucleus from the oocyte comes into close proximity with the nucleus from the spermatocyte.

...