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Whether you are aware of your incessantly ticking biological clock or not, the absolute last thing that any woman of steadily advancing childbearing age wants to hear when she flips on the morning news shows is: Women lose 90 percent of their eggs by age 30.

Thirty? Life has hardly begun at 30! Gulp.

The hard truth is that decades of research have proved that a woman's fertility declines over time. But now it appears that the old biological clock may start ticking much earlier -- and faster -- than once thought.

A study from the University of St. Andrews and Edinburgh University, published last month by PLoS ONE, tracked the human ovarian reserve -- or a woman's potential number of eggs -- from conception through menopause. Using a mathematical model and data from 325 women, the researchers found that the average woman is born with around 300,000 eggs and steadily loses them as she ages, with just 12 percent of those eggs remaining at the age of 30, and only 3 percent left by 40.

"That's a greater percentage of loss at an earlier age than had previously been reported," says reproductive endocrinologist Robert Stillman, of Shady Grove Fertility in Rockville. "One might be able to argue whether there are 12 percent remaining at age 30 or 22 percent or even 40 percent, but it is still clear that there's a very rapid loss in the number of eggs available as women age and that the smaller pool of [older] eggs is also more likely to" contain a higher proportion of abnormal eggs, he adds, pointing out that from the mid-30s on, the decline in fertility is much steeper with each passing year.

"This adds to the abundant evidence that for women, unfortunately, it's use 'em or lose 'em."

Before you start freaking out, it's important to remember that even 30,000 or so eggs remaining at the start of your 30s is still a lot. In addition, the quantity and quality of eggs are just two factors affecting fertility: Plenty of women get pregnant perfectly easily in their 30s and even early 40s. Also, infertility technology has come a long way in even the past decade. Still, given that a study published last year in the journal Fertility and Sterility found that female undergraduates significantly overestimated their fertility prospects at all ages, it seems wise for women thinking about starting a family -- or having more children -- to educate themselves about aging's effects on conception and pregnancy.

"I think the important message is: Don't leave [having a child] too late, if it is something that is going to be very important to you, " says W. Hamish Wallace, a co-author of the Fertility and Sterility study. An oncologist at the Royal Hospital for Sick Children at the University of Edinburgh, he says he hopes this research will help doctors advise young cancer patients on how best to preserve their fertility after treatment and improve counseling for healthy women.

The biological reality that female fertility peaks in the teens and early 20s can be difficult for many American women to swallow, as they delay childbirth further every year, according to the National Center for Health Statistics. In the District, the average age of initial childbirth was 26.5 years in 2006, up 5.5 years since 1970, the highest jump in the country.

"While we may not be mature enough to conceive at a young age, nor should we, that is still when the body is most adept at conception and carrying a baby," says Claire Whelan, program director of the American Fertility Association. "Our biological clock has not kept pace with our ability to prolong our life spans." Stillman agrees, pointing out that research about advanced maternal age and motherhood today is clear: The older you get, the more difficult it is to get pregnant and the higher the chance of miscarriage, pregnancy problems such as gestational diabetes and hypertension, and chromosomal abnormalities such as Down syndrome, among other concerns. A study published this month in Autism Research found that the risk of autism increases with a mother's age: Women over 40 were 77 percent more likely than those under 25 to have a child with the condition. (There was also an elevated risk when the dad was over 40 and the mother was in her 20s.)

"Society has changed, " says Stillman, "but the ovaries will take another million years or two to catch up to that."

Since we don't have another million years to wait, many women thinking of having children are left with the predicament of balancing the personal, primal urge to partner up and procreate with worthwhile social goals such as pursuing higher education and a successful career -- not to mention economic stability.


It doesn't make it any easier that the media are filled with mixed messages on women's fertility: Compare the studies filled with doom-and-gloom statistics on advanced maternal age and pregnancy with the myriad photos of 40- or 50-something celebrities in glossy magazines, gleefully holding their bouncing baby, projecting the image that fertility isn't as finite as it seems.

"In some ways, medicine has done too good a job, " says Stillman, who notes that at Shady Grove, the oldest woman to get pregnant using her own eggs gave birth at 44, while the clinic will help women use donor eggs up until 51, the average age of menopause.

"If you're going to be on the cover of People, you need to be honest and say you're using donor eggs, because other women look at that and say, 'I can wait till I'm 50, 51,' and they are sadly mistaken."

There are at least a few things worth noting in the meantime: While the PLoS ONE study on ovarian reserve found that age alone affected a woman's store of eggs up until 25, lifestyle factors such as stress, smoking and being overweight can have an increasingly negative impact on fertility as you get older, say the authors and AFA's Whelan.

"You can't prolong your biological clock -- you're not going to produce more eggs -- but that's not the only factor around fertility," Whelan explains. "Women do need to start thinking proactively about their own reproductive health, and protecting it, as time passes."

Staying healthy in general may give you a bit of leeway, in other words, but being realistic -- and in the know -- could be the best medicine of all.