Medical Examiner

Fertile Ground

Is there any way to predict a woman’s reproductive lifespan?

Illustration by Robert Neubecker

These days, it’s hard to open a magazine without reading about some novel development in infertility medicine: A doctor performs transplants of the uterus (albeit in mice); couples pay to choose the sex of their baby. But most of the wizardry of infertility technology—such as in vitro fertilization, the formerly revolutionary, now quotidian procedure in which egg and sperm are merged in a Petri dish, and the resulting embryos transferred to the woman’s uterus—has, understandably, been focused on helping those who are having trouble getting pregnant to do so.

Yet as one of the millions of women who are now, by choice or circumstance, postponingpregnancy, I became curious: If you’re a woman who’s not yet trying to conceive, but may someday want to, is there any way to know your future fertility?

Right now, the answer is no. While this might seem surprising, it isn’t so odd when considered in the context of the fertility business. Fertility clinicians, after all, are trained to diagnose and treat existing fertility problems—not to screen for future ones. And if the great majority of their patients want to be pregnant yesterday—and will pay high sums to be so—why should they take time to conduct highly experimental research for those who might want to be pregnant tomorrow?

As it happens, a few fertility researchers are now taking the time. Teams at Erasmus Medical Center and Utrecht University—both in the Netherlands—and (if funding comes through) at the University of California at San Francisco, are now, or will soon be, investigating methods that might one day be used to predict a woman’s reproductive lifespan and answer that anxiety-inducing question that plagues so many women today: How many fertile years do I have left?

As we’ve all heard, fertility declines with age: By the time a woman reaches her late 20s, it may take a little longer for her to conceive; by her mid-to-late 30s, it can become dramatically more difficult. And by her early 40s, harder still.

Of course, these are only population averages; reproductive lifespan differs wildly among women. But how to identify individual women who are potentially at risk for an early end to fertility? Perhaps, researchers say, via methods used now to diagnose and treat infertility.

For all women, the general decline in fertility that comes with age seems to stem in good part from the decline in what’s called “ovarian reserve”—the quality and quantity of a woman’s eggs. A woman is born with a finite number of eggs; over time, her supply dwindles, due to what doctors call “ovarian aging.”

Today, infertility clinicians often infer a woman’s ovarian reserve by measuring blood levels of a host of reproductive hormones. This is done in order to predict her short-term odds of success with ovulation-inducing drugs used in infertility treatments. The hormones linked to ovarian reserve include follicle-stimulating hormone (or FSH), along with lesser-knowns such as inhibin B and antimullerian hormone. High blood levels of FSH on specific days of the menstrual cycle may indicate that there has already been a decline in egg quality and quantity. Low levels of inhibin B on these days may also indicate a similar signal of a decline, as may low levels of antimullerian hormone.

An alternate method of assessing ovarian viability is using an ultrasound to observe the numbers of antral (or developing) follicles in the ovaries. During each menstrual cycle, a certain number of egg-containing follicles will reach this antral stage. Researchers hypothesize that the higher the antral follicle count, the better the odds are that a woman can get pregnant.

Some doctors already offer antral follicle counts or FSH tests to women not yet trying to conceive in order to provide a sense of their current—not future—ovarian reserve. But there is much to learn before such methods can be applied with full confidence to women in the general population. For one thing, most studies investigating these methods have thus far been done on women undergoing infertility treatments, who may not respond to the tests in ways identical to women in the general population. For another, most of the studies have not tracked women over the long haul.

In studies like the one at UCSF, then, researchers will follow a group of 1,250 women to try to discern “normal” hormone levels and antral follicle counts at various ages—as well as whether changes in hormone levels and ultrasound results occur at a predictable rate. They will also try to determine whether these markers provide an early enough warning to give a woman time to try to get pregnant before her fertility wanes.

While we wait for answers—the UCSF study will not conclude for another five years, and some researchers I spoke with suggested that an ideal (if unrealistically expensive) study would last for “decades”—it’s easy to start speculating about how such screening tests might affect the culture at large.

Would they convince women to settle for Mr. Maybe? Or would women finally have the ultimate life-scheduling tool, one that allowed for seamless, premeditated transitions from full-time work to full-time motherhood—and back again?

While many women would find the tests to be valuable for this reason, the notion of knowing one’s reproductive senescence can sound a bit Brave New World-ish. As a female friend said to me, “I wouldn’t want to know my ‘sell-by’ date.”

In any event, ovarian-reserve screening tests would never solve all the mysteries of reproduction. The ability of any given couple to conceive without technological assistance depends on factors other than the number of healthy eggs. In men, these can include anatomical and sperm abnormalities; in women, uterine problems, say, or blocked fallopian tubes.

For now, then, instead of looking to technology for data it can’t reliably provide, perhaps we should ponder the low-tech information that is readily available. Among women who turn to in vitro fertilization and its ilk—a category called assisted-reproductive technologies, or ART—success rates dwindle dramatically as a woman ages. For instance, in 2001, ART cycles in 32-year-old women resulted in a live-birth (or births) 36.8 percent of the time. By comparison, only 11.4 percent of ART cycles in women aged 41, for which the woman used her own (not a donor’s) eggs, resulted in a live-birth. One infertility doctor recommended to me that everybody who’s 30 should spend a day in an IVF clinic, just to observe the experience. “You’re going to see so much misery,” he told me, “that you’ll go home and throw your pills out the window.”

Or maybe you won’t. Not every woman desires children. But knowing for certain that you don’t desire children and won’t later in life regret not having them—if only there were a test for that.