You want to eat—and avoid—all the right foods and drinks when you're pregnant. Sometimes, it's hard to know what you can and can't have.
Hard cheeses are okay; soft cheeses are to be avoided. Salmon is great for growing babies; swordfish isn't. And what about coffee?
The American College of Obstetricians and Gynecologists (ACOG) and other experts say that it's safe for pregnant women to consume up to 200 milligrams of caffeine a day. That's the equivalent of one 12-ounce cup of coffee.
A new study suggests that even a small amount of caffeine can impact birth weight.
Women who consumed an average 50 milligrams of caffeine per day—just a quarter of the recommended limit—gave birth to babies who were 2.3 ounces lighter than babies born to women who didn't drink any caffeine, according to the March 2021 report published in JAMA Network Open.
The study followed more than 2,000 women at 12 clinical sites in the United States. Researchers asked the expectant mothers to estimate their caffeine intakes and also used blood samples taken during the first trimester to determine the exact levels ingested.
Most of the women involved in the study reported drinking 200 milligrams or less of caffeine per day. Just 0.7% of the women estimated that they drank more than the recommended daily amount.
Overall, pregnant women with the highest blood levels of caffeine gave birth to babies that were about 3 ounces lighter, 0.17 inches shorter, 0.11 inches smaller in head circumference, and about 0.13 inches smaller in thigh circumference than the infants of women with no or minimal caffeine in their systems.
Researchers say their study shows that even small amounts of caffeine consumption can impact a baby's birth weight.
So what does that mean for you, mama? Should you go cold-turkey and ditch coffee and soda altogether?
"It's hard to make recommendations based on the results of one study," says Diana Spalding, CNM, midwife and Motherly's Maternal Health Advisor. "We need to pay attention certainly, but recommendations might not change right away."
Doctors make their expert recommendations based on years of data—not just a single study.
Birth weight is complex—there are a lot of factors that can affect a baby's weight. Spalding wonders, for example, if factors that lead to people drinking more coffee during pregnancy need to be evaluated as well. "Is someone drinking coffee in pregnancy because they enjoy it or because they work the night shift and have a toddler to take care of? If it's the latter, could that impact fetal growth?"
Ultimately, experts say that more research needs to be done to fully understand exactly how a mother's diet and caffeine intake affect her baby.
Until then, if you have any questions—consult your doctor or midwife. It's always best to discuss your concerns with medical professionals who know you and your medical history.
"It can be stressful to hear results like this. It's always best to talk directly with your provider about your specific circumstances. Ultimately, trust that you are doing the best you can with the information available."
Gleason JL, Tekola-Ayele F, Sundaram R, et al. Association Between Maternal Caffeine Consumption and Metabolism and Neonatal Anthropometry: A Secondary Analysis of the NICHD Fetal Growth Studies–Singletons: A Secondary Analysis of the NICHD Fetal Growth Studies–Singletons. JAMA Netw Open. 2021;4(3):e213238. doi:10.1001/jamanetworkopen.2021.3238
A version of this story was originally published on March 26, 2021. It has been updated.