ATLANTA, Georgia (CNN) -- New research out Monday may have expecting moms rethinking their drinking habits.
During pregnancy, caffeine can inhibit blood flow to the placenta.
A new study has found that pregnant women who consumed more than 200 milligrams of caffeine a day, equivalent to about two cups of coffee, had twice the risk of miscarriage as the women who consumed no caffeine at all. The findings are published in Monday's Journal of Obstetrics and Gynecology.
Previous studies have found similar results, but Dr. De-Kun Li, lead author and investigator with the Kaiser Permanente Division of Research, is quick to point out the significance of his findings. "We were able to address the issue of if the increase is really due to caffeine or due to women changing their drinking patterns. Other studies have reported the same results but had some biases in the research."
Just how much is 200 milligrams of caffeine? We did the math for you.
Amounts are estimates; actual caffeine content may vary by brand
The Kaiser study looked at 1,063 women in the early stage of pregnancy. Among women who consumed no caffeine, the miscarriage rate was 12.5 percent. In comparison, 25.5 percent of women who consumed more than 200 mg of caffeine a day miscarried. Although there was an increased risk for women who consumed fewer than 200 mg of caffeine a day, the lead investigator says the increase is not statistically significant.
Researchers say it made no difference whether the caffeine came from coffee, soda, tea or hot chocolate.
Caffeine is dangerous during pregnancy, Li said, because it can cross through the placenta to the fetus and can be difficult for the fetus to metabolize the caffeine. Caffeine may influence cell development and decrease blood flow to the placenta, he added. If arteries are constricted it may restrict blood flow which can result in miscarriage.
Dr. Jennifer Wu, a New York obstetrician who has no ties to this study, said the research is, "accurate and has found a definitive correlation between caffeine consumption and miscarriage." Wu says expecting moms should significantly decrease the intake of caffeine during pregnancy. Watch Dr. Wu discuss caffeine and pregnancy »
Current recommendations from the March of Dimes warn women not to exceed 300 milligrams of caffeine a day. Other groups, including the American College of Obstetricians and Gynecologists, tell CNN they do not have a recommended guideline for caffeine consumption during pregnancy. Their Web site says, "There's no proof that small amounts of caffeine (for instance, one or two cups of coffee) harm the fetus."
Li hopes this study will lead ACOG and other organizations to reevaluate the current guidelines. E-mail to a friend
Danielle Dellorto is an associate producer with CNN Medical News.
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