Whether you are aware of your ticking biological clock or not, the last thing that any woman of steadily advancing childbearing age wants to hear when she turns on the morning news show is: women lose 90 per cent of their eggs by age 30.
Thirty? Life has hardly begun at 30! Gulp.
The 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 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 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 12 per cent of those eggs remaining at the age of 30, and 3 per cent 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 Maryland, US. “One might be able to argue whether there are 12 per cent remaining at age 30 or 22 per cent or even 40 per cent, 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 that from the mid-30s on, the decline in fertility is 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 30,000 or so eggs remaining at the start of your 30s is a lot. In addition, the quantity and quality of eggs are just two factors effecting fertility: Plenty of women get pregnant easily in their 30s and even early 40s. Infertility technology has also come a long way in the past decade.
Still, it seems wise for women thinking about having 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, co-author of the Fertility and Sterility study. An oncologist, he says he hopes this research will help doctors advise young cancer patients on how best to preserve their fertility after treatment and improve counselling 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 every year, according to the National Centre for Health Statistics.
But Stillman says that research today is clear: The older you get the higher the chance of miscarriage, pregnancy problems, such as gestational diabetes and hypertension, and chromosomal abnormalities such as Down syndrome.
A study published this month in Autism Research found that women over 40 were 77 per cent more likely than those under 25 to have a child with autism. (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, women thinking of having children are left with the predicament of balancing the primal urge to partner up with goals such as pursuing education and a successful career.
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 a negative impact on fertility as you get older, say the study's authors.
“Women do need to start thinking proactively about their own reproductive health, and protecting it, as time passes,” says AFA's director Whelan.
In other words, staying healthy in general may give you a bit of leeway but being realistic and in the know could be the best medicine of all.
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