Women who drink two cups of coffee during pregnancy face twice the risk of miscarriage, according to a new study.
Although prior studies have suggested a link of caffeine to miscarriages, this is the first time the effects of morning sickness have been screened out.
The research found a higher rate of miscarriage in women who consumed more than 200 milligrams of caffeine a day - the amount in two cups of home-brewed coffee, or three cups of tea. Because drinks at coffee bars usually contain higher levels of caffeine, a single serving there might deliver 150-200 milligrams.
The research was reported by lead investigator Dr. De-Kun Li, a reproductive and perinatal epidemiologist with Kaiser Permanente's Division of Research in Oakland, Calif. It was reported in the Journal of Obstetrics and Gynecology.
"This study strengthens the association between caffeine and miscarriage risk because it removes the speculation [it] was due to reduced caffeine intake by healthy pregnant women," Li said.
"The main message for pregnant women," he said, "is that they probably should consider stopping caffeine consumption during pregnancy because this research provides clearer and stronger evidence that high doses of caffeine intake during pregnancy can increase the risk of miscarriage."
In the study, Li's team interviewed 1,063 women who had been pregnant a median of 71 days. Of those, 172 miscarried, a typical rate of about 16 percent. But the rate was 12.5 percent for those who had abstained from caffeine and 24.5 percent for those who had more than 200 milligrams a day.
Based on the study, the March of Dimes plans to change its advice to pregnant women to limit their caffeine intake to 200 milligrams a day, but other experts showed doubts about the findings.
"Moderation is all things is still an excellent rule," Dr. Carolun Westhoff, a professor of obstetrics and gynecology at Columbia University Medical Center, told the New York Times. "I think we tend to go overboard on saying 'Expose your body to zero anything when pregnant.' The human race wouldn't have succeeded if the early pregnancy was so vulnerable to a little bit of anything. We're more robust than that."