On coffee and miscarriages

How worried should women be about caffeine intake during pregnancy?

By Catherine Price

Published January 22, 2008 4:40PM (EST)

Is your daily cup of coffee raising your chances of a miscarriage? That's what a study, published Monday in the American Journal of Obstetrics and Gynecology, suggests. According to the New York Times, the study -- which was based on 1,063 pregnant women in California -- suggests that pregnant women who consume more than 200 milligrams of caffeine a day may be doubling their risk of miscarriage.

Now, I am not a medical professional, researcher or miscarriage specialist. But this report, which currently tops the list of most e-mailed articles on the Times' Health page, does make me wonder about a few things. First is the question of how accurate the women were in reporting the amount of caffeine they consumed. Nutritionists have long observed that people frequently underestimate how many calories they eat each day. I would think that the same could be true for caffeine consumption. Maybe you forget a refill of coffee, or leave out a cup of tea, or eat a bar of dark chocolate as an afternoon snack. Maybe one cafe's "small" is another's "medium." And maybe it has nothing to do with your reporting at all -- caffeine content can vary a great deal, depending on how long you brew the coffee or tea, and what kind it is. Sure, there's a standard amount of caffeine in some products, like a can of Coke, but if I, for example, were to report to you that today I had a small decaf iced coffee from Peet's, one and a half cups of decaf coffee at a diner and one-half cup of caffeinated coffee at the same diner, how the hell would you calculate my caffeine intake? (Keep in mind, I use a lot of milk.) It seems like there's a lot of room for error.

Also, as the Times reports, there might be some confusion in the cause and effect going on. The article points out that women who report having morning sickness have a lower risk of miscarriage than those who don't, partially because the same hormones associated with morning sickness are associated with healthy pregnancies. (And yes, if there's a God, he or she has a sense of humor.) If you're feeling nauseous, you might not crave your usual triple latte -- which would lower your reported caffeine intake, and which might mean that you mistakenly associate your healthy pregnancy with your lowered caffeine consumption rather than with hormonal shifts that made you crave less caffeine to begin with.

I bring this up partially because other articles on the study do not report these potential conflations. Take NPR's "Morning Edition" report, for example. It points out that different cups of coffee have different caffeine content, but it doesn't mention anything about how women's hormones or chromosomal abnormalities might have more to do with miscarriage than the beverages they consume.

I'm not saying that previous studies linking high caffeine consumption and miscarriages must be wrong -- I just think it's important to consider other variables as well. So for anyone who heard NPR but missed the piece in the Times, here's the most important excerpt, perspective-wise:

"Dr. Carolyn Westhoff, a professor of obstetrics and gynecology, and epidemiology, at Columbia University Medical Center, had reservations about the study, noting that miscarriage is difficult to study or explain. Dr. Westhoff said most miscarriages resulted from chromosomal abnormalities, and 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, chlamidial 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.'"

Catherine Price

Catherine Price is an award-winning journalist and author of Vitamania: How Vitamins Revolutionized the Way We Think About Food. Her written and multimedia work has appeared in publications including The Best American Science Writing, The New York Times, Popular Science, O: The Oprah Magazine, the Los Angeles Times, The San Francisco Chronicle, The Washington Post Magazine, Salon, Slate, Men’s Journal, Mother Jones, PARADE, Health Magazine, and Outside. Price lives in Philadelphia.

MORE FROM Catherine Price

Related Topics ------------------------------------------

Broadsheet Coffee And Tea Love And Sex Pregnancy