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How Long Can You Really Wait to Have a Baby?


Almost no woman is a stranger to her "biological clock," but it turns out women in their 30s may not have as much to worry about as we thought.

Last week in a piece for The Atlantic, psychologist Jean Twenge scoured medical research databases and took a broad look at numerous published studies on fertility. She found that many cited statistics aren't necessarily wrong but that they are based on old and outdated information.

For example, a 2004 study published in Human Reproduction suggests that 1 in 3 women aged 35 to 39 won't get pregnant after a year of trying. The source of the data? French birth records from 1670 to 1830.

"Most people assume these numbers are based on large, well-conducted studies of modern women, but they are not," Twenge writes. "When I mention this to friends and associates, by far the most common reaction is: 'No…no way. Really?'"

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According to Twenge, there are few large-scale, well-designed fertility studies that include women born in the 20th century, and of the ones that do, the data are more optimistic. In fact, a 2004 study published in Obstetrics & Gynecology found that 82 percent of 35- to 39-year-old women got pregnant, compared to 86 percent of 27- to 34-year-olds.

Some experts say we should proceed cautiously. Fertility peaks in a woman's 20s, says Philip Chenette, M.D., fertility specialist at Pacific Fertility Center. "We know women in older age groups take longer to conceive and have higher risks of miscarriage and aneuploidy."

Unfortunately, the data available is based mostly on historical data and IVF outcomes, Dr. Chenette says. "We're developing techniques to improve our ability to predict, but this is a work in progress. Individualizing that prediction for an individual is problematic today. We just don’t know, for an individual, how and when her fertility will begin to decline with age and the fact that some women get pregnant easily in their 30s doesn't mean that will be true for all."

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Conducting studies on natural conception is tough, writes Twenge, because there are so many factors at play: Modern birth records are often uninformative because women who get pregnant in their 20s then tend to use birth control to prevent later pregnancies, studies that ask people to remember how long it took them to conceive are unreliable (human memory is a tricky thing!), and finding and studying women who are trying to get pregnant is hard because there's such a narrow window between when they'll try and when some will succeed, she says.

However, Twenge doesn't dispute the fact that fertility does decline with age, and she suggests having your last child by age 40. "Beyond that, you’re rolling the dice, though they may still come up in your favor."

For most healthy women, optimizing their fertility can be achieved through lifestyle changes, Dr. Chenette says. "Pursue a good diet, try to reduce the amount of stress in your life, avoid excessive alcohol, and don't smoke."


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