Published in BMJ Evidence-Based Medicine, the study used past research in an attempt to demystify the relationship between maternal caffeine consumption and adverse pregnancy outcomes like miscarriage, low birth weight, stillbirth, pre-term delivery, childhood leukemia, and childhood obesity. "There is substantial cumulative evidence of an association between maternal caffeine consumption and diverse negative pregnancy outcomes," says author of the study Jack E. James, PhD, a professor at Reykjavik University. "Consequently, current evidence does not support health advice that assumes 'moderate' caffeine consumption during pregnancy is safe."
Not all reproductive health experts and gynecologists agree with this conclusion, however—and that's because there are a lot of obstacles when it comes to measuring how much a cup of tea or coffee can really affect a pregnancy. "Unfortunately, all of the data on pregnant women and caffeine are from basically observational trials," says Mary Jane Minkin, MD, a gynecologist and clinical professor of obstetrics, gynecology, and reproductive sciences at Yale University. "These studies are observing real women going through pregnancies and asking about caffeine consumption—they are not prospective, randomized, double-blind trials that we like to do with medications to change one variable and see what happens." When you're just observing people, there's no real way to control the experiment to zero in on the consequence (if any) of consuming caffeine.
Lucky Sekhon, MD, fertility specialist and board-certified OBGYN from NYC, points out that these studies prove even more flawed because of the natural biases that happen in trials that can't be finely controlled by researchers. "The majority of studies on caffeine use in pregnancy, to date, rely on pregnant women to recall their caffeine consumption before and during their pregnancy, which is often a significant time after they having been pregnant," she says. "There is often 'recall' bias in this case, where women who had an adverse outcome in pregnancy have a greater tendency to recall and possibly exaggerate their exposure to caffeine during pregnancy."
These studies often also overlook confounding factors that could lead to worse health outcomes. "For instance, women who consume very high levels of caffeine may be from a lower socioeconomic background or have a tendency to also be smokers or take on additional exposures that contribute to adverse pregnancy outcome," says Dr. Sekhon. For all of these reasons, the ACOG already sent out a note to its members saying that Dr. James' review didn't strike them as a reason to alter their current recommendations. And Dr. Sekhon agrees that's a good call.
"To say that [caffeine] should be avoided at all costs during pregnancy, in my opinion, is an over-extrapolation of the data and not necessary," says Dr. Sekhon. "I tell women it is okay to consume caffeine in pregnancy, but the daily amount should not exceed 200 milligrams. It is important to be aware of the caffeine contact of not just beverages such as tea or coffee, but also in food."
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