Pregnant women who consume two or more cups of coffee per day face a higher miscarriage risk than women who avoid caffeine, a study finds.
In the late 1990s, researchers at the Kaiser Foundation Research Institute in Oakland, Calif., interviewed 1,063 women less than 15 weeks pregnant. Of these, some consumed no caffeinated beverages during pregnancy, some consumed at least 200 milligrams (mg) of caffeine daily, and the rest consumed less. The average cup of coffee contains about 75 to 135 mg of caffeine, while tea and soft drinks aren’t as potent.
Women ingesting 200 mg of caffeine or more per day in any form were roughly twice as likely to miscarry during the first 20 weeks of pregnancy as were those getting no caffeine. Women consuming less caffeine faced no increased risk. The report appears in the March American Journal of Obstetrics & Gynecology.
The scientists accounted for age, race, education, household income, marital status, smoking status, alcohol consumption, hot-tub use, and differences in morning sickness—a factor seldom included in studies of this type.
Nausea might lead some women to change their caffeine intake during pregnancy, so the researchers focused only on women who maintained their caffeine-use patterns during pregnancy.
Some scientists have also wondered whether women with nausea represented a healthier-pregnancy group, since morning sickness stems from potent hormones that ostensibly would help a fetus develop. By eliminating the morning-sickness variable, the new study establishes an effect by caffeine, says study coauthor De-Kun Li, an epidemiologist at Kaiser.
Caffeine alters normal cell functions and reduces blood flow to the fetus. But beyond that—and that it can pass through the placental barrier—its effects on a fetus remain poorly understood.