Women with ovulatory dysfunction (irregular or even absent menstrual cycles) will benefit from the use of fertility drugs to induce ovulation. In addition, couples with unexplained infertility may use ovulation induction as a way of increasing the number of mature follicles released. Gonadotropins (FSH and LH) are hormones that function by stimulating the ovaries to produce follicles, each of which contains an egg. Gonadotropins are synthesized and released by the pituitary gland, a small gland located at the base of the brain. The pituitary produces two different types of gonadotropins: luteinizing hormone (LH) and follicle stimulating hormone (FSH). Both of these hormones act on the ovaries in a coordinated fashion to recruit and develop ovarian follicles.
Ovulation induction works by increasing the amount of follicle stimulating hormone (FSH) that reaches the ovary. The source of FSH can be endogenous (coming from within the body—specifically coming from the pituitary gland) or exogenous (coming from outside the body—specifically coming from injections). Oral medications for ovulation induction rely on endogenous sources of FSH.
There are essentially two choices of oral ovulation induction medications used in the U.S.—Clomiphene (Clomid) or Letrozole (Femara). Both work by tricking the brain to send out more FSH. They usually result in the production of one mature follicle per cycle but it can produce more than one. Monitoring sonograms are used during the cycle to follow the progress of the developing follicles. There is a risk for twins when taking these medications (Clomid 5-8%, Femara 3-5%).
Exogenous forms of FSH include the medications Gonal-F, Follistim, and Bravelle, which are all given by injection. Injectable medications can also have a combination of LH and FSH (i.e. Menopur). Ovulation induction using these types of medications is often referred to as superovulation. Sonogram monitoring needs to be more frequent as the risk for multiple mature follicles is increased. The risk of twins is increased up to 30%. Sometimes superovulation OI cycles need to be canceled, especially when too many mature follicles are present.