Just half a cup of coffee a day may cause pregnant women to give birth to smaller babies

BETHESDA, Md. — There’s an old myth that caffeine will stunt your growth, especially in children. While science has yet to prove this is true, a new study finds it may affect a baby’s birth weight. Researchers say pregnant women drinking as little as half a cup of coffee daily may give birth to smaller babies.

Previous reports have discovered potential risks to the fetus among mothers-to-be drinking over 200 mg of caffeine daily. The new report finds similar connections between reductions in size and lean body mass when drinking less than two cups of coffee a day. Smaller birth size can create higher risks for obesity, heart disease, and diabetes later in life.

The study reveals babies born to women with the highest blood levels of caffeine were, on average, three ounces lighter. The infants were also 1.7 inches shorter and had smaller head circumferences than those born to caffeine-free mothers.

Study authors are now urging women to give up coffee or caffeine products during pregnancy as their research continues.

“Until we learn more, our results suggest it might be prudent to limit or forego caffeine-containing beverages during pregnancy,” says Dr. Katherine Grantz from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) in a media release.

“It’s also a good idea for women to consult their physicians about caffeine consumption during pregnancy.”

Is caffeine dangerous for unborn babies?

Previous studies have pointed to a number of health issues possibly caused by caffeine use during pregnancy. Along with being smaller inside the womb, researchers say caffeine may impact the brain and cause behavioral issues after birth.

Fetuses are also at higher risk for intrauterine growth restriction; being in the lowest tenth percentile for infants of the same gestational age. Until now however, studies on moderate daily caffeine kicks, meaning two coffees or less, during pregnancy have produced mixed results.

“Some have found similar elevated risks for low birth weight and other poor birth outcomes, while others have found no such links,” researchers explain in their report.

The current research shows many of the earlier studies did not account for factors that could influence infant birth size. These include variations in caffeine content of different drinks and maternal smoking during pregnancy. In the new study, researchers analyzed data on more than 2,000 racially and ethnically diverse women at 12 clinical sites. Each of the women enrolled between their eighth to 13th week of pregnancy and were healthy non-smokers before getting pregnant.

Even a little caffeine can have a major impact

From weeks 10 to 13 of pregnancy, the women provided blood samples later checked for caffeine and paraxanthine — a compound produced when caffeine is broken down in the body.

Participants also reported their daily consumption of caffeinated drinks including coffee, tea, soda, and energy drinks over the past week. The group did this once when they enrolled and then periodically throughout the rest of their pregnancies.

Compared to infants born to women with little or no caffeine their systems, infants born to women with the highest blood levels of caffeine were consistently lighter and shorter. Based on the women’s own estimates of the drinks they had, women who consumed around half a cup of coffee (50 mg of caffeine) had infants about 2.3 ounces lighter than infants born to non-caffeine drinkers. Similarly, babies born to regular caffeine drinkers also had thigh circumferences about 0.13 inches smaller than others.

“Caffeine is believed to cause blood vessels in the uterus and placenta to constrict, which could reduce the blood supply to the fetus and inhibit growth,” the researchers write. “Similarly, researchers believe caffeine could potentially disrupt fetal stress hormones, putting infants at risk for rapid weight gain after birth and for later life obesity, heart disease and diabetes.”

The findings appear in the journal JAMA Network Open.

SWNS writer Laura Sharman contributed to this report.