How long can you wait?

To have a baby that is.  Really, really good story on the matter in the Atlantic.  I read it at the beach (overlooking the Atlantic ocean, no less) and have been meaning to give it a good blog post ever since, but since I haven’t yet, it’s time to give it at least a half-assed blog post.  Short version: I thought I knew a lot about fertility statistics, but it turns out not nearly as much as I thought.  Women’s fertility certainly does decline after 30, but not nearly as dramatically as I had been led to believe.  This bit was easily the most eye-opening:

The widely cited statistic that one in three women ages 35 to 39 will not be pregnant after a year of trying, for instance, is based on an article published in 2004 in the journal Human Reproduction. Rarely mentioned is the source of the data: French birth records from 1670 to 1830. The chance of remaining childless—30 percent—was also calculated based on historical populations.

In other words, millions of women are being told when to get pregnant based on statistics from a time before electricity, antibiotics, or fertility treatment. Most people assume these numbers are based on large, well-conducted studies of modern women, but they are not. When I mention this to friends and associates, by far the most common reaction is: “No … No way. Really?

The studies using modern data paint a much more optimistic picture:

Surprisingly few well-designed studies of female age and natural fertility include women born in the 20th century—but those that do tend to paint a more optimistic picture. One study, published in Obstetrics & Gynecology in 2004 and headed by David Dunson (now of Duke University), examined the chances of pregnancy among 770 European women. It found that with sex at least twice a week, 82 percent of 35-to-39-year-old women conceive within a year, compared with 86 percent of 27-to-34-year-olds. (The fertility of women in their late 20s and early 30s was almost identical—news in and of itself.) Another study, released this March in Fertility and Sterility and led by Kenneth Rothman of Boston University, followed 2,820 Danish women as they tried to get pregnant. Among women having sex during their fertile times, 78 percent of 35-to-40-year-olds got pregnant within a year, compared with 84 percent of 20-to-34-year-olds. A study headed by Anne Steiner, an associate professor at the University of North Carolina School of Medicine, the results of which were presented in June, found that among 38- and 39-year-olds who had been pregnant before, 80 percent of white women of normal weight got pregnant naturally within six months (although that percentage was lower among other races and among the overweight). “In our data, we’re not seeing huge drops until age 40,” she told me…

In Dunson’s study of modern women, the difference in pregnancy rates at age 28 versus 37 is only about 4 percentage points. Fertility does decrease with age, but the decline is not steep enough to keep the vast majority of women in their late 30s from having a child. And that, after all, is the whole point.

My two younger sisters were born when my step-mom was 38 and 40.  I’ve always thought how lucky she was to conceive with no issues at that age.  Turns out, she wasn’t lucky, but actually fairly normal.  Now, I think there’s plenty of reasons to go ahead and have those kids before late 30’s if a woman is in a healthy relationship– and her odds to get worse, just not dramatically– but I have to say, this really does revise a lot of what has become conventional wisdom on fertility.

About Steve Greene
Professor of Political Science at NC State

3 Responses to How long can you wait?

  1. Henrietta Jenrette says:

    Even if fertility rates are close between young and older, the rate of birth abnormalities does increase. Is that the case or are the stats based on the same studies that gave us old information on fertility? We are also told that the age of the father is related to a woman’s fertility and the rate of fetal abnormalities. I think that is pretty current research.
    So how about a study of the relationship between age of mothers and rate of fetal defects? Fertility is not the only thing to consider when dalaying pregnancy.

  2. Karen Kay says:

    Speaking of fertility worries, I’m conducting my psychology dissertation research on worry about future fertility among women 25 to 40 years old, and I launched my survey this week! The survey deals with a lot of the issues brought up in this Atlantic article. Please check it out and consider passing it on to your contacts. Thank you!

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