Lack of producing a good quality egg is a frequent cause for infertility, particularly as a woman ages. Deterioration of egg quality occurs at different rates in women. While poor quality eggs occur less frequently in young women, the variability in loss of good quality eggs among women makes it an important parameter to assess in all infertile couples, regardless of age.
When a woman is born, her ovaries will contain her entire life’s supply of eggs. These are continually lost through menstruation until the woman reaches menopause, the point when the ovarian reserve is empty. Women over the age of 37 or who have undergone ovarian surgery have an increased risk of infertility due to a diminished ovarian function or reserve (fewer healthy eggs due to natural aging).
The term “ovarian reserve” refers to a woman’s remaining egg supply that can produce babies. A woman’s fertility depends on the quality and quantity of eggs in her ovaries, as well as how well the ovarian follicles are responding to hormonal signals from the brain. In the absence of other fertility factors, ovarian reserve is the most important predictor of a woman’s pregnancy potential.
Regular menstrual cycles are a good indication that ovulation is occurring normally. If a woman’s period comes infrequently or not at all, then her ovulation is either uncommon or simply not occurring. Since human reproduction is inherently inefficient (couples generally have a 20 percent chance of becoming pregnant in any given menstrual cycle). This leads to fewer opportunities to become pregnant and also makes it difficult to predict ovulation in order to time intercourse.
Hormone levels are the outward signs of ovulation. Several tests that check for normal ovulation rely on measuring these hormones. The main tests for ovarian reserve are follicle-stimulating hormone (FSH), estradiol, anti-mullerian hormone, and an ovarian antral follicle count. These tests are generally performed early in the menstrual cycle, usually on the second or third day after the start of full menstrual flow.
Follicle-stimulating hormone (FSH) helps control the menstrual cycle and egg production. FSH levels are tested on day 2 or 3 of the menstrual cycle to determine a woman’s ovarian function and evaluate egg quality.
In general, women with elevated FSH levels found in their blood on day 2 or 3 of the menstrual cycle have reduced chances of having a live birth – even with ovulation induction and in vitro fertilization (IVF) – compared to other women of the same age.
Currently, there are several different laboratory methods used to measure FSH blood levels, and the hormone level measured may vary considerably from one method to the next. Therefore, it is difficult to compare blood level tests between different laboratories or if the test was performed using a different technique.
For this reason, it is important that normal and abnormal test values be based on the pregnancy rates achieved by women studied using the same laboratory methods at a particular center.
In conjunction with the FSH test, a woman’s ovarian function and quality of eggs can be evaluated through testing estradiol, an important form of estrogen. This test is also performed on day 2 or 3 of the menstrual cycle.
Anti-mullerian hormone (AMH) is produced by individual follicles (a normal cyst that contains an egg) in the woman’s ovary. The more eggs and therefore the more follicles a woman has, the higher the anti-müllerian hormone levels that can be measured. As a woman ages, however, and egg number decreases, so does the anti-mullerian hormone level. This test is usually performed on day 2 or 3 of a normal menstrual cycle along with the FSH and estradiol hormone level tests and the antral follicle count. Since values for AMH do not vary during a menstrual cycle, if it is the only test that needs to be obtained, it can be drawn at any time. AMH is a very powerful predictor of ovarian reserve and has replaced a number of other tests such as the Clomiphene citrate challenge test.
Antral (small) follicles are about 2-8 mm in diameter and can be seen, measured, and counted by ultrasound. Vaginal ultrasound is the best way to accurately assess and count these small structures, also called resting follicles. The number of antral follicles visible on the ultrasound indicates the estimated number of immature eggs, with each follicle containing one egg that has the potential to develop in the future. If only a few antral follicles are visible, then the corresponding egg numbers are also low.
During an in vitro fertilization (IVF) procedure, the patient is injected with follicle stimulating hormone (FSH) to stimulate the maturation of the antral follicles in order to retrieve the developed eggs. More eggs retrieved equals better IVF success, but if there are only a few antral follicles to begin with, very few eggs will be collected, and IVF has a decreased chance of working.
Ovarian reserve tests are not absolute infertility indicators, but abnormal hormone levels do mean there will probably be a lower response to ovulation induction medications, and thus lower IVF treatment success rates.