PGD, IVF, and Fertility Drugs

Preimplantation genetic diagnosis, PGD, is a procedure conducted as a part of an in vitro fertilization, IVF, cycle. IVF requires stimulation of the ovaries with follicle stimulating hormone (FSH) to cause the recruitment of multiple follicles, each of which contains an egg. Numerous eggs are needed for an IVF cycle as some may be damaged during the various IVF processes.

In order to understand how FSH (Gonal-F, Follistim, Repronex, etc.) stimulates the ovaries, it is necessary to have a basic understanding of how reproductive hormones (HPA axis) exert their effects. The hypothalamus is a small gland located at the base of the brain that can be compared to a "thermostat". It monitors the levels of hormones, such as FSH, LH, estrogen, and others. As it monitors these hormones, it increases or decreases their production based upon a "feedback" mechanism.

During the first days of the menstrual cycle, the hypothalamus produces gonadotropin-releasing hormone (GnRH) , which travels to the pituitary where it stimulates the production of follicle stimulating hormone. FSH causes the recruitment of ovarian follicles and supports them as they mature. As the follicles grow they begin to produce estrogen, which travels through the bloodstream to the hypothalamus. Estrogen also helps stimulate and support the development of the endometrium.

Rising levels of estrogen cause the hypothalamus to reduce its production of GnRH thus lowering FSH levels. Once the follicle(s) is mature, the hypothalamus signals the pituitary to release a surge of LH, which triggers ovulation. The ruptured follicle remaining after ovulation forms a structure known as the corpus luteum, which begins to produce progesterone to support the pregnancy. Once the embryo has implanted the placenta also begins producing progesterone.

Patients undergoing PGD also receive the medication Lupron, Cetrotide, or Ganirelix, which prevents premature ovulation. If ovulation occurred prior to egg retrieval, the cycle would by "lost". These drugs "down regulate" the pituitary causing reduced production of FSH and LH. Ovulation cannot occur until an injection of LH or hCG is administered. The eggs are retrieved, fertilized, and incubated until ready for the PGD procedure.

Once the biopsied PGD embryos are ready for transfer and injection of hCG is given and transfer to the uterus is scheduled accordingly.