Ovarian Function

Women are normally born with two ovaries, which contain a lifetime supply of eggs. Once menses begins at puberty, eggs develop within the ovarian follicles on the ovary and are ovulated during each monthly menstrual cycle.

The menstrual cycle is controlled by the interaction of several hormones in the biologic system known as the "hypothalamic-pituitary-adrenal axis". The hypothalamus is located at the base of the brain and is responsible for monitoring and adjusting hormone levels by sending feedback to the pituitary gland. The pituitary produces many hormones including follicle stimulating hormone which stimulates egg development.

During the first days of the ovulatory cycle, the hypothalamus produces gonadotropin releasing hormone (GnRH). GnRH travels to the pituitary where it stimulates the production of follicle stimulating hormone (FSH). FSH stimulates the ovaries to "recruit" eggs and then supports their development.

As the eggs within the follicles mature, they begin to produce increasing amounts of another hormone, estrogen. Estrogen levels rise signaling the hypothalamus to reduce production of FSH as the eggs approach maturity. Estrogen also stimulates the development of the endometrium (lining of the uterus) which must become thick and vascular to support the developing embryo.

Once the eggs mature, the hypothalamus signals the pituitary to produce a large surge of leutinizing hormone (LH). LH triggers ovulation, or the release of the egg from the ovarian follicle. The egg travels through the fallopian tube to the point of fertilization at the distal end.

After ovulation, the residual follicle develops into a structure known as the corpus luteum and begins production of progesterone. Progesterone also stimulates and supports the development of the uterine lining. Once pregnancy occurs, the placenta begins to produce progesterone to support the endometrium during an ongoing pregnancy.

Anovulation is the lack of ovulation and oligoovulation is irregular ovulation. Ovulatory irregularities are a common cause of infertility and can be caused by hormone abnormalities, which can result from diseases such as PCOS. Abnormal ovulation can also be caused by too much exercise and stress.

Eggs have a fertilization capability that is related to age and individual genetic factors. As the eggs age, the level of FSH rises and is measured on day 3 of the menstrual cycle. Levels above 12 mcg/ml are indicative of the onset of menopause or perimenopause. The clomiphene citrate challenge test is also used to measure "ovarian reserve", or the eggs fertilization and development capability. Many fertility clinics will not perform IVF with women who fail the clomiphene citrate challenge test because success rates are very poor.

Ovulatory irregularities are often treated with Clomid (clomiphene citrate). Clomid works at the hypothalamus by competing with estrogen. Lower levels of estrogen signals the hypothalamus to increase production of GnRH with increases production of FSH.

If pregnancy has not occurred after 3-6 cycles of Clomid, injectable FSH is usually the next step. FSH stimulates the ovaries directly causing the production of many eggs. Numerous eggs are necessary for ART procedures such as IVF.

FSH should be administered by a specialist thoroughly trained in its use. Dosages must be monitored and adjusted to prevent side effects, such as hyperstimulation syndrome and multiple births.

If the eggs will not fertilize due to poor ovarian reserve or other factors, donor egg is usually the best option. Donor egg recipients have the same IVF success rates at the age group of the donor. For example, if a 22 year old woman's eggs are used and the success rate for this group is excellent, the recipient will have a 40% to 70% chance of pregnancy. This percentage varies according to the clinical practice rates as well as the couple's specific medical history.

In women under 35, most ovulatory disorders can be effectively treated with medications and/or lifestyle changes. (Read More- Age and Infertility)