"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.)