Checking Your Biological Clock

The FSH test, which is generally considered the standard test, measures the follicle-stimulating hormone. During the first, or follicular, phase of the menstrual cycle, the part of the brain known as the hypothalamus releases a hormone that tells that pituitary gland to release FSH. The hypothalamus and the pituitary gland know whether the follicles have been stimulated because the maturing egg secretes estrogen into the blood stream. If a woman's FSH level is elevated on the third day of her menstrual cycle, that suggests that her ovarian reserve is reduced because the pituitary gland is having to release an excess amount of the hormone in its effort to stimulate the ovaries.

Physicians caution, however, that FSH test results are not a definitive assessment of fertility. "The FSH test is really only reliable when it's abnormal, so a reassuring day 3 FSH test does not assure fertility," says Janis Fox, MD, director of egg donation at the Brigham and Women's Hospital in Boston.

That is due, in part, to the fact that the eggs that are responding to FSH might not be of good quality. At the same time, an abnormal, or elevated, test result does not mean a woman won't be able to conceive. "You can have an elevation in FSH and still be fertile; the younger you are, the less predictive FSH levels are."

The CCCT test may provide additional information in women over the age of 35 with unexplained infertility who have normal FSH test results. This test measures FSH and estrogen levels at day three of a woman's cycle and again at day 10, after she has taken clomoiphene (Clomid), a medication that induces egg production. If the FSH levels are still high, that may indicate a diminished ovarian reserve.

While not as widely used, the inhibin-B test measures inhibin-B, which is a hormone secreted by certain cells in the ovaries; low levels of this hormone are associated with low pregnancy rates.

The Size of the Eggs

The Human Reproduction study suggests that ovarian volume may reflect the number of follicles remaining in the ovaries, and that this may help determine ovarian reserve and therefore reproductive age. Ovarian volume, which is the size of the ovaries in three dimensions, can be measured with transvaginal ultrasound, a sonogram conducted with a vaginal probe. By analyzing large studies, the researchers found that smaller ovaries and a low number of follicles per ovary correlates with a low ovarian reserve, while larger ovaries and a high number of follicles correlates with a higher ovarian reserve.

Advice to Clock Watchers

Dr. Sharara says that these study findings are good news for all women interested in their fertility to get a sense of their "reproductive age." "If you come in at 35 and you get an ultrasound done, and your ovaries look great, then you may be able to wait, let's say, a year or so, taking into account what happens to the ovaries as women get older than 35."

"But if you want to wait three, four years, for whatever reason, to have a child, and you do this test and your ovaries don't look that healthy, you may really want to rearrange your priorities," he continues.

Dr. Fox, however, does not think there is sufficient evidence to justify using the test in the general population, and notes that the quality of the eggs cannot be adequately assessed with the ultrasound. "It's not a crystal ball: I wouldn't feel comfortable saying wait another year."

After all, in addition to the difficulty in accurately assessing ovarian reserve, there are factors other than ovarian reserve that can affect fertility, including gynecological conditions such as endometriosis, exposure to sexually transmitted diseases and infertility in a male sexual partner.

"You need to be aware of age," Dr. Fox cautions, "and the biological clock does go off a lot sooner than a lot of women think, but the idea that you can measure and predict the moment when you have to get pregnant is not true."