Although current health advice assumes moderate caffeine consumption during pregnancy is safe, the author of the recent meta-analysis found the evidence compelling enough to conclude that pregnant women and women contemplating pregnancy should avoid caffeine altogether.
Heightened Risks
For the analysis, Jack James, PhD, a professor of psychology at Reykjavik University in Iceland, looked at 48 studies focused on maternal caffeine consumption in the past two decades. He found that 32 of them suggested caffeine-related increased risk in four main categories:
MiscarriageStillbirthLow birth weightChildhood acute leukemia
Although some previous studies have looked at preterm birth as an additional risk, James didn’t find enough evidence to add that to the list.
How Caffeine Works During Pregnancy
To understand the potential harms of caffeine on a fetus, James writes that it’s important to look at the main mechanisms of action that come with caffeine consumption. Whether in beverage or food form, caffeine easily crosses the placenta barrier, exposing the fetus to the drug, James notes. This has been proven by other research, most notably by a study published in April in the European Journal of Nutrition that analyzed hair samples of newborns and found traces of caffeine consistent with the amount that mothers had during pregnancy. That study indicated that the higher the caffeine consumption, particularly in the third trimester, the higher the amount in the newborn hair samples, giving an indication of fetal cumulative caffeine exposure. That third-trimester nod is especially crucial, writes James. During pregnancy, a woman’s metabolism changes, which means she’s able to clear caffeine from her system in the first trimester similar to before getting pregnant. But as the pregnancy progresses, the rate of clearance slows to about half in her second trimester and just one-third in the last trimester. “Consequently, caffeine half-life increases from the usual adult rate of about five hours in the first trimester to about 18 hours by the 38th week of pregnancy,” James states. Because the substance stays in the body longer, it raises more risk for a fetus.
Effect of Caffeine on Newborns (and Mothers)
Previous research from the late 1980s and early 90s indicates that being born with caffeine in their systems affects newborns, including caffeine withdrawal symptoms such as disturbed sleep, irritability, increased frequency of irregular heartbeat, respiration issues, more vomiting, and higher risk of tremors, similar to babies born to mothers who take narcotics. The good news, according to one of the older studies, was that symptoms resolved on their own, similar to caffeine withdrawal in adults. But the less-stellar news from the recent meta-analysis is the risks during pregnancy, James states, and he points out that even though caffeine is very widely consumed around the world, it’s still considered a drug. “Chronic exposure to chemicals during pregnancy is cause for concern—the need for caution with caffeine is compelling,” James states, adding that the substantial evidence of an association between maternal caffeine consumption and diverse, negative pregnancy outcomes should raise some alarms. With some studies, James says, there’s no threshold of consumption where negative outcomes don’t exist to some degree. In other words, caffeine might be the exception to the “everything in moderation” mantra.
Role of Stress
Not covered in the recent study but part of the concern is the amount of stress during pregnancy, which is very common, according to dietitian Erin Kenney, MS, RD. “In addition to the metabolism changes during pregnancy that make caffeine stay in the system longer, caffeine also stimulates secretion of the catecholamine stress hormones of epinephrine and norepinephrine,“ Kenney says. “Depending on how much stress the mother is already in, this load can be overbearing. When these stress hormones are released, they can potentially increase placental vasoconstriction and increase fetal heart rate, leading to impaired fetal oxygenation.“ There does appear to be a dose-related response, she adds, which means that more consumption leads to more risk, so low consumption may not be as much of a concern. For women who are healthy, non-stressed, with a balanced lifestyle, good gut health, on-point hormonal levels, and a nutritious diet, Kenney would likely recommend that 200 mg of caffeine daily would be generally safe. That’s about two 8-ounce cups of brewed coffee, depending on factors like what type of coffee beans are used and how they’re prepared. However, even then, pregnant women should keep in mind that the slowing rate of clearance during the second and third trimester might mean making the switch to decaf.
