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Remember Kids, Correlation does Not Equal Causation


It’s a simple rule of middle school math: correlation does not equal causation. So why is it that when it comes to pregnancy, reporters, doctors and researchers let this simple dictum go right out of their heads?

Exhibit A: a new study released this weekend shows that there may be a correlation between caffeine intake and miscarriage. And the NY Times springs into action, immediately posting an article that leads with the breathlessness that makes pregnant women–and other people–nuts. In the article, the study’s lead author follows up her results with recommendations that pregnant women give up caffeine completely for 3-4 months because, as she puts it, “stopping caffeine doesn’t really have any downside.” Well, she hasn’t seen me before my coffee in the morning, but that’s another story.

So, the perfect pregnancy panic continues. The March of Dimes has already changed its caffeine recommendations for pregnant women, based solely on this study, the results of which are–at best–suggestive of some sort of correlation between coffee intake and miscarriage. At worst, it’s a study with flawed methodology (women were interviewed about their caffeine intake only once and the majority after they miscarried. What’s more, even if there is an actual correlation, I can imagine myriad other causes besides caffeine that could cause miscarriage. Perhaps women who drink more coffee during pregnancy are also less well-rested, have higher stress jobs or lives, or face other factors in their daily lives that lead them to drink multiple coffees a day. Maybe they’re law students.

Thankfully, there is one voice of reason in the panic over perfect pregnancy. Dr. Carolyn Westhoff, a professor at Columbia Medical School and the director of their family planning clinic rides to the rescue:

“[Dr. Westhoff] said that most miscarriages resulted from chromosomal abnormalities, and that there was no evidence that caffeine could cause those problems.

‘Just interviewing women, over half of whom had already had their miscarriage, does not strike me as the best way to get at the real scientific question here,’ she said. ‘But it is an excellent way to scare women.’

She said that smoking, chlamydial infections and increasing maternal age were stronger risk factors for miscarriage, and ones that women could do something about.

‘Moderation in all things is still an excellent rule,’ Dr. Westhoff said. ‘I think we tend to go overboard on saying expose your body to zero anything when pregnant. The human race wouldn’t have succeeded if the early pregnancy was so vulnerable to a little bit of anything. We’re more robust than that.’

Finally, someone is cutting through the BS and reminding us all that maybe, just maybe, we’ve become a little insane about the demands we place on pregnant women — perfect pregnancies, perfect births, perfect babies.

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