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Study finds moderate daily caffeine intake may lead to smaller babies

The study shows that even smaller amounts of caffeine impact a baby's size. Still, more research needs to be done to understand it better.
Pregnant woman with coffee beans
Caffeine consumption during pregnancy is an often studied topic, yet most pregnant people remain confused as to what advice is best.TODAY Illustration / Getty Images
/ Source: TODAY

When it comes to consuming caffeine during pregnancy, moms-to-be often feel confused. Some think it's best to cut it out completely while others seem content to have a 12-ounce cup of coffee every morning. A new study in JAMA Network Open looks at caffeine consumption and birth weight and found that even women who enjoy less than the recommended amount of caffeine can have slightly smaller babies.

“There’s been a lot of conflicting information out there,” Jessica Gleason, an author of the paper, and member of Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, told TODAY. “We are able to look at a wide range of new neonatal size and growth measures … What's also unique about our sample is that they really didn't drink that much caffeine.”

Researchers examined data from 2,055 participants who are part of a longitudinal cohort study. On average, participants were about 28 years old, had a healthy body mass index and did not smoke. The researchers asked participants to report how much caffeine they consumed, a common way to determine caffeine use. But the researchers also went a step further and performed a blood test that indicated how much caffeine the pregnant women had by examining the amount of metabolite produced when the body breaks down caffeine. This gives a more accurate picture.

“A lot of prior research has self-reported caffeinated beverage intake, which a lot of times will miss, for example, decaffeinated beverages, which do contain small amounts of caffeine, and also chocolate and other sources of caffeine,” Gleason explained.

The study found that women who drink even less than 200 mg of caffeine a day, about a 12-ounce cup of coffee — the current recommendation from the American College of Obstetricians and Gynecologists — do have babies who are about 84 grams or three ounces smaller than women who have consumed no caffeine. Lower birth weight could contribute to diabetes, obesity and heart disease, noted Gleason.

“We can’t make recommendations based on the results of a single study but we would always encourage pregnant women to talk to their providers about caffeine consumption,” Gleason said. “There is some suggestion that caution may be warranted.”

Dr. Hyagriv Simhan, who did not participate in the study, said the study adds to experts’ understanding of how moms' caffeine use impacts their babies.

“It is consistent with what we know about the biology of caffeine, and it's association with the growth of babies,” the division director of maternal fetal medicine and medical director of obstetrical services at Magee-Women’s Hospital of UPMC in Pittsburgh told TODAY. “We've acknowledged an effect or relationship, not causal per se, but an association of caffeine intake and fetal growth from other studies and papers … this (paper) is unique in terms of demonstrating this effect along the continuum of caffeine consumption.”

While the paper shows that even lower amounts can impact fetal development, Simhan said it’s still unclear what that means. He says birth weight is complex and it’s hard to know what smaller birth weight means for the babies with moms who had caffeine. The experts agree that more research needs to be done to fully understand it. But does this study mean that pregnant women should skip their 12-ounce cup of java?

“Often pregnant women and the public in general pay attention to studies like this because they're worried about risks,” Simhan said. “It's fair to say that while there is an effect of caffeine intake on fetal growth. We don't know the implications of that.”

He says that women should always talk to their doctors or midwives when they have questions about caffeine and pregnancy.

“I've been doing this long enough to know when studies like this come out, it promotes lots of phone calls to the office,” he said. “That's what the provider patient relationship is for — to put these studies in the context of (helping) people make individual personal decisions.”