Actually, Women Are Quite Fertile Until Their 40s

Both popular and scientific consensus is that female fertility peaks around 27 years of age, then drops sharply such that by 35, the odds of getting pregnant are not good, and by 40, they’re virtually non-existent. However, that conclusion is actually based on some very questionable data: French birth records from around the 18th century. More recent studies show that women aged 35-39 have somewhere around an 80% chance of getting pregnant within a year of trying, which is roughly 5% less than younger women.

The top left graph, from a 2002 issue of TIME magainze, is likely wrong. The American Society for Reproductive Medicine does not cite their source.

The top left graph, from a 2002 issue of TIME magainze, is likely wrong. The American Society for Reproductive Medicine does not cite their source.

 

Why is the modern medical community relying on 200 year-old data? Because, thanks to modern science, modern birth records are useless: most women now have children in their 20s and then use birth control to stop having children in their 30s, after they’ve had a couple. Instead of looking at records, scientists could just study some people to get statistics, but it’s hard to find large numbers of women trying to get pregnant, especially since that window is generally less than six months. And asking them later to remember how long it took is very unreliable. Not to mention that a large number of women over 35 who are trying to get pregnant are only doing so because they were infertile when they were younger — most people are not that careful about getting pregnant.

So, the choice is between data from a time when there were no antibiotics, fertility pills, or even proper nutrition, and data from a time where birth control makes study subjects scarce. The latter is still probably better, but the three modern studies on fertility included only 400 women over 35, which is that representative of the global population. And besides its age, a big problem with the historical data is that, in the 1700s, people likely would stop having much sex after having had a few kids in their 20s, which would make the data look like women were infertile in their 30s when really, they were just not having sex.

All things considered, the modern data is a lot more reliable than the historical one. Also, most fertility problems are not related to the woman’s age, but rather blocked tubes, endometriosis, or male infertility. The take-away is this: women in their 30s do experience more miscarriages, but are only slightly less fertile than in their 20s.

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