The Delicate Balance of Pregnancy Research

The Delicate Balance of Pregnancy Research

December 2021

“Pregnant women CAN drink coffee – it could even slash risk of disease for mum and baby,” proclaimed a headline in the English paper The Sun about a recent study in JAMA Network Open. While lead researcher Stefanie Hinkle, PhD, is happy to be the bearer of good news, she hopes that readers burrow down to find the more nuanced story that follows in smaller type below.

“We can say that caffeine consumption within current recommendations for pregnant women isn’t increasing risk — and appears to be actually lowering risk — for gestational diabetes. And we see no increased risk for pre-eclampsia or gestational hypertension — which can both be severe complications. That’s all positive, but it’s only one piece of the story,” she notes. In fact, last summer, a team including Dr. Hinkle — who then worked at the National Institute of Child Health and Human Development (NICHD) — published a very different JAMA Open paper based on the same set of data. In that paper, the researchers concluded that caffeine consumption, even in amounts less than the 200 mg per day maximum that the American College of Obstetricians and Gynecologists recommends during pregnancy, was associated with smaller neonatal measurements.  

Both papers stemmed from the same longitudinal cohort study, the National Institute of Child Health and Human Development Fetal Growth Studies–Singletons, which enrolled 2055 nonsmoking US women between 2009 and 2013. The initial purpose was to look at fetal growth, but the team also collected lots of other information: about diet, activity, sleep and caffeine.

The summer paper did show that for several measurements, the newborn babies of mothers who consumed caffeine were smaller — but the results also served as another reminder about how much more remains to be discovered about diet during pregnancy. “The long-term implications of our findings are unclear, considering the relatively small estimates we observed,” the researchers wrote.

The mother's caffeine metabolism slows during pregnancy, they noted, and because the fetus lacks CYP1A2 enzymes for metabolism, caffeine and paraxanthine accumulate in fetal tissues. They wondered if these disruptions might put children at higher risk for rapid weight gain after birth, for childhood obesity, and for later cardio-metabolic disease.

Their latest study, now in process, may shed light on those questions. In this paper, led by Jessica Gleason, PhD, MPH, at NICHD, the team is looking at a group of children from this same cohort, at ages four to eight. Dr. Hinkle sees these children as additional participants, whose health interests highlight just how pregnancy research is a multilayered pursuit.

“That’s the tricky part in this research: There’s maternal health, and then there’s fetal health. You have two sets of stakeholders. Ideally what’s good for one is good for the other, but that’s not always the case.” She expects the team to publish the results of the study on young children’s health sometime in 2022.


Stefanie Hinkle, PhD; Jessica L. Gleason, PhD, MPH; Samrawit F. Yisahak, PhD; et al

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