It can be a heartbreaking scenario. A couple decides it’s time to have a baby, and it appears that all systems are go. Her menstrual cycles are fairly regular; he has a healthy sperm count. Yet, they fail to conceive. The culprit, seen in about 15 percent of infertile couples, may be low ovarian reserve—too few eggs left in the ovaries. This means that conceiving naturally is decidedly more difficult, though not necessarily impossible.
Ovarian reserve declines throughout a woman’s life as part of the natural aging process that leads to menopause around age 50. “Every woman has a predetermined, probably genetic, rate of ovarian aging,” explains Beth Rackow, M.D., assistant professor of obstetrics and gynecology at Yale University School of Medicine, New Haven, Connecticut. Fertility declines naturally with age in large part because the supply of eggs in the ovaries decreases. But sometimes the decline happens a lot quicker than what’s considered normal, affecting women still in their 20s or 30s. And young women with a diminished egg supply may not know anything is wrong until they are unable to conceive and eventually wind up at a fertility clinic for testing.
Low ovarian reserve can be detected by a simple blood test taken between days 2 and 5 of a woman’s cycle. The test measures follicle stimulating hormone (FSH), which is produced by the pituitary gland to stimulate the follicles that grow eggs in the ovaries. If the follicles don’t mature properly and respond to the hormone, the pituitary continues to pump out even higher levels of FSH to try and get the follicles to respond. That’s why a high blood level of FSH is linked with a low number of follicles (or eggs). FSH can fluctuate from month to month, so a doctor should order repeat tests, especially if the first result is borderline. Generally, a FSH level over 15 is considered high, though this can vary from lab to lab.
“We’re noticing now that [low ovarian reserve] is a factor in what we used to call unexplained infertility,” says Nanette Santoro, M.D., chair of the department of obstetrics and gynecology at the University of Colorado at Denver. “If you have had a workup and there is nothing wrong with your tubes, you’re ovulating, and your partner has a good sperm count, then you should have FSH tested at least once.”
