by F. Nicholas Shamma, MD

Ovulation occurs in the woman each month due to a number of hormonal and anatomical changes. Several parts of your body are involved in the process of ovulation. The brain sends hormonal signals telling the ovaries to produce an egg each month. A hormone called gonadotropin releasing hormone (GnRH), which is produced in an area of the brain called the hypothalamus, acts on the pituitary gland to produce follicle stimulating hormone (FSH) and luteinizing hormone (LH). These two hormones then act on the ovaries to help produce the growth and development of an egg in a process called ovulation.

Women are born with a finite number of eggs. At birth, a woman has around 1 to 2 million eggs. However, throughout her life, a woman loses eggs through a destructive process called atresia. At puberty, only around 400,000 eggs remain. Throughout the reproductive lifespan, from puberty until menopause, women lose about 1,000 eggs each month.

Of these thousand eggs, only one is released. Once released, it is picked up by the fallopian tube. If a couple has sexual intercourse around this time, fertilization (the joining of the egg and sperm) may take place. The fertilized egg, called an embryo, finds its way to the uterus where it gets implanted in the uterine wall and develops into a fetus. The fetus develops over a period of about nine months and, if all goes well, a healthy, happy baby is delivered.

Ovulation induction is a process whereby -- through drug therapy -- some of the 1,000 eggs lost monthly are rescued from atresia and allowed to develop to maturity. The following discussion is a description of the process of ovulation induction.

When is Ovulation Induction Used?

There are various reasons why a woman might need to undergo ovulation induction. Though the goal is always to promote ovulation, the treatment itself changes depending upon the woman's particular situation.

Hypothalamic-pituitary dysfunction

Some women are given medications to replace some or all of the hormones that are produced by the pituitary gland. Such a situation occurs when a woman has had surgery on the pituitary gland, or more commonly has a pituitary gland that is unable to produce the hormones FSH and LH. This latter scenario may happen when a woman loses a significant amount of weight in a condition known as anorexia nervosa. It also may occur when women exercise excessively or are under a considerable amount of psychological stress. Under these conditions, although the pituitary gland is normal, it does not produce FSH and LH. All of these circumstances fall under the category of ovarian dysfunction called hypothalamic-pituitary dysfunction.

Several hormonal treatments are currently available to women who cannot produce FSH and LH. These medications are called gonadotropins. These gonadotropins are given by injection either into the muscle or under the skin. Two major forms of these medications are currently available. One form contains an equal amount of FSH and LH. This medication is available in the United States under the trade names Humegon, Pergonal, or Repronex. These forms, which contain LH and FSH extracted from the urine of postmenopausal women, are usually given by injection into the muscle. The other form of this medication is a newly developed product made of genetically engineered FSH. This medication is available in the United States under the trade name of Gonal F or Follistim. This product can be injected under the skin, a much easier and much less painful way of administering the medication.

With gonadotropin therapy, you usually start the medication on the third day of the menstrual cycle, with day 1 representing the first day of the menstrual bleeding. The medication is continued for an average of 10 days. During this period, ultrasound examinations of the ovaries are regularly performed to monitor the growth of the follicles. The follicle is the structure within which the human egg, or oocyte, develops. When it is determined by ultrasound that the follicles have reached maturity, the final trigger of ovulation, human chorionic gonadotropin or hCG, is given to release the eggs. Because this process involves the release of multiple eggs, more than one egg may be picked up by the fallopian tube, and fertilized. If all of these implant, it would result in a multiple gestation, i.e. twins, triplets, or even more.

There is another ovulation induction regimen that can be utilized by women who are experiencing hypothalamic-pituitary dysfunction. This involves utilizing a hormone known as GnRH. This hormone acts on the pituitary gland causing it to produce LH and FSH. This medication is either given in the vein (intravenously) or under the skin via a pump. The pump, however, is cumbersome and seldom used in the United States.

Polycystic ovarian syndrome

This is a more common syndrome in which the brain can produce FSH and LH, but the ovaries do not respond normally to these hormones, and therefore do not develop a mature egg each month. Doctors call the inability to produce an egg each month "chronic anovulation". Polycystic ovarian syndrome usually occurs in women who are overweight and have excess body hair, oily skin, and sometimes acne. Such women will not produce the ovarian hormones estrogen and progesterone which are necessary for the uterus to produce a menstrual period each month. As a result, they have long and irregular menstrual cycles or no menstrual periods whatsoever. One of the recent advances in polycystic ovarian syndrome is the finding that some of the women with this syndrome have a high insulin level in their blood, a condition known as hyperinsulinemia. This is due to an inability of the body's insulin to work effectively (called "insulin resistance").