Biological Alarm Clock

Currently the rule of thumb is that most women go through menopause at about the same time as their mothers. But there are variations. Once women hit about 45 and start experiencing erratic periods or hot flashes, "it's not brain surgery" to figure out the woman is well on her way to the menopause, says Dr. Wulf Utian, executive director of the North American Menopause Society.

But for women younger than 45, diagnosis can be a little trickier. Hormone tests, such as the follicle-stimulating hormone or FSH test, may be used when a woman younger than age 45 experiences symptoms such as erratic periods or hot flashes. But FSH levels can fluctuate daily, which can complicate a diagnosis.

The new AMH model could improve predictions to "plus or minus one to two years," says lead author Dr. Jeroen van Disseldorp. And it would be most appropriate for women who are 30 years old, since AMH levels seem to rise until the third decade of life—the point when many women may be making decisions about whether to postpone pregnancy in favor of a career, van Disseldorp says.

Though the AMH research is in its early stages and results have to be validated in different populations, knowing how long a woman's biological clock will keep running would be important information. "Everyone is looking for a marker as to when menopause will happen, not when it's [already] happened," says Utian. "This [AMH] test isn't ready for prime time, but it could be beneficial." For one thing, it might get women to pay closer attention to heart and bone health earlier in life: menopause brings with it an increased risk of osteoporosis and heart disease. But the big payoff, of course, would be in helping predict or avert fertility problems.

The biological reality is that eggs don't stay fertile forever. Women are born with about 1 million eggs in their ovaries. At age 20 the average woman has about 200,000 eggs. By age 40 that number has dropped to less than 20,000. Egg quality starts to decline at about age 30, takes a sharp drop at about age 35, and by about age 40 almost half of all women are not able to have a baby naturally, says Dr. David Adamson, president of the American Society for Reproductive Medicine.

Despite advances in assisted reproductive technologies, the optimal time for a woman to get pregnant is before age 35. "Don't shoot the messenger, but that's a reality, and it's one that some women who want children don't want to hear," says Adamson. "Eggs deteriorate. You can't take reproduction for granted."