Pregnant women are often confused about caffeine consumption. Is a cup of tea OK? What about an espresso? A diet soda? A new meta-analysis published in the journal BMJ Evidence-Based Medicine finds a correlation between caffeine consumption and adverse pregnancy outcomes. But experts say women shouldn’t toss their reusable coffee mug and shun all caffeine just yet.
“People should not be panicked by this information. They should not feel guilty, like ‘I am four weeks pregnant and I had coffee,’” Dr. Stacy Beck, an assistant professor in the department of obstetrics, gynecology and reproductive sciences, maternal fetal medicine at the University of Pittsburgh, told TODAY. “(Caffeine consumption) is a conversation you should have with your obstetrician or midwife who oversees your care."
Jack James, a professor in the psychology department at Reykjavik University in Iceland and author of the research, examined the findings from 37 observational studies published over the last two decades, looking specifically at caffeine consumption and pregnancy outcomes in what’s known as a meta-analysis, an assessment of previous research to glean any conclusions from the larger body of work. He found that past research indicates that moderate-to-high consumption in pregnant women shared a correlation with negative pregnancy outcomes.
“The majority of relevant peer-reviewed studies report that caffeine is associated with increased risk of negative pregnancy outcomes, including miscarriage, stillbirth, lower birth weight, small for gestational age, childhood acute leukemia, and childhood overweight and obesity,” James told TODAY via email. “Certainly, there is no evidence to suggest that caffeine benefits either mother or baby. Therefore, even if the evidence were merely suggestive, and in reality it is much stronger than that, the case for recommending caffeine be avoided during pregnancy is thoroughly compelling.”
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While this warning seems dire, experts suggest that the research about caffeine is far from as conclusive as James suggests. The meta-analysis relied on past research so it isn’t providing any new data about the relationship between caffeine and pregnancy.
“Nothing in this article is really different from anything we knew,” Beck said. “Almost all of the studies are older studies, they are retrospective studies. They looked back in time and talked to women about caffeine consumption."
That means women reported how much caffeine they consumed during pregnancy after the fact, which isn’t always the most reliable information as it's subject to human error. What’s more, Beck said most people think of caffeine only being in coffee or tea, but it is often in other products so many women would seriously underreport their consumption. Most studies involved women who spoke with a reproductive endocrinologist or their doctor about their health prior to pregnancy and this skews the population.
“That alone significantly limits the type of people this data is coming from — educated women who are not low income. That tends to be the type of patient to talk to their doctor to review their health information,” Beck explained. “That is a huge limitation.”
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Anecdotally, women who are older often drink more caffeine and those who drink more caffeine also smoke and drink alcohol more frequently, Beck and Oster stressed. Age, alcohol consumption and smoking also contribute to negative outcomes in pregnancy. So the cause of negative pregnancy outcomes could be unclear in some of the research.
“If all the studies have the same problem, then you’re not really fixing the problem by averaging all the studies,” Emily Oster, an economics professor at Brown University in Providence, Rhode Island, and author of Expecting Better, told TODAY. “You can say every study shows the same thing. Well, all of them have the same problem.”
The American College of Obstetricians and Gynecologists has issued a committee opinion that says pregnant women can enjoy less than 200 milligrams of caffeine per day because it “does not appear to be a major contributing factor in miscarriage or preterm birth.” This recommendation comes from reviewing past studies much like those featured in this paper. Pregnant women cannot participate in randomized controlled trials where one group consumes caffeine and another does not. This causes a natural limitation on the research on caffeine and pregnant women.
“Pregnancy has been an exclusion,” Beck explained. “Groups of experts come together and look at the same studies and analyze them and make an expert opinion based on consensus.”
The recent paper also looks at correlation not causation, which finds an association between caffeine consumption and negative pregnancy outcomes not as cause and effect.
“There is not a direct link,” Beck said. “None of these studies prove a causative effect.”
Still James believes the evidence is strong enough for experts to recommend that pregnant women should not consume caffeine.
“It is simply not plausible to suggest that current evidence implicating caffeine is so flawed as to be capable of being ignored. In fact, there is a large body of consistent evidence from well-controlled studies pointing to caffeine as a source of harm during pregnancy,” he said.
But Dr. Adam Jacobs, associate director of biostatistics at Premier Research, a clinical research company based in North Carolina, said that the researcher failed to disclose his conflict of interests.
“I note the author has published two books on the dangers of coffee, which in my opinion should have been included in declarations of interest for the journal article," he told the Science Media Centre, a London-based nonprofit organization.
Oster said that she found the paper's conclusion to be unusually strong.
"The statements in this paper are extreme for a paper that is a meta-analysis of studies where we know that there’s a reasonable amount of bias,” she explained.
TODAY contacted the researcher for a comment on these criticisms, but did not immediately hear back.
Bottom line: Worried women should talk to their doctors about their caffeine consumption during pregnancy.
“If you feel anxious about this after reading, I would just go talk to your doctor … This is a place where your doctor can help you work through it,” Oster said. “You could also read the guidelines and recognize that this is not new evidence.”