In other panic-inducing news last week: too much caffeine may increase the chance of miscarriage. The new study  found that pregnant women who consume 200 milligrams or more of caffeine a day--the amount in 10 oz. of coffee, 25 oz. of tea, or seven cans of soda--may double their risk of miscarriage.

Multiple studies in the past have come to differing conclusions about how risky caffeine is in early pregnancy. A review of the best studies of caffeine and pregnancy to date was published in 2005. This review discussed how many problems those studies have--and their results are only as good as their data. The authors concluded that it's difficult to draw a firm conclusion about a link between caffeine and miscarriage. As a result, doctors, the American College of OB/GYNs, and even the March of Dimes have advocated moderation. Six cups of coffee may be "too much," but there is likely no problem with a cup or two of caffeinated coffee each morning.

This latest study suffers from some of the same problems as previous ones. It didn't enroll a lot of women, and more than half of them had already had a miscarriage. It relies on people's memories of how much coffee and soda they drank--and we're notoriously unreliable at accurately recalling our diets.       

The vast majority of miscarriages come from chromosomal abnormalities, or a problem at the most basic genetic level, and there is no evidence that caffeine can interfere at that point. There are some known risk factors for miscarriage: cigarette smoking, chlamydial infections and getting older. So women who want to maximize their chances of pregnancy success can focus on the things that we know can make a difference.

I think it's important that doctors make recommendations based on good evidence--if not, we lose all credibility.  So much advice docs have given over the years was shown to be misguided later: Eggs are bad! Margarine is good! Red wine is bad! In the end, I'm telling my patients to stick with caffeine moderation--pregnancy is hard enough as it is.