Small doses of caffeine may not increase miscarriage risk

November 24, 1999
Web posted at: 6:20 PM EST (2320 GMT)

By Sarah Yang

(WebMD) -- Though high-octane doses of caffeine can double a pregnant woman's risk of miscarriage, she may be able to indulge in a daily latte or two safely, according to a study published in this week's New England Journal of Medicine.

The research, conducted by the National Institute of Child Health and Human Development (NICHD), is the latest entry in the debate over caffeine consumption during pregnancy.

Past studies on animals and humans have given conflicting results about how much caffeine is safe for a pregnant woman. Some have shown an increased risk of prenatal problems from just one or two cups of coffee a day; others have shown no rise in risk even from large amounts of caffeine.

"This debate has been going on for quite a while," says Mark Klebanoff, M.D., lead investigator and director of the Division of Epidemiology, Statistics and Prevention Research at the NICHD. "My intention was to try to look at this in a new way."

Klebanoff chose not to rely on questionnaires to gauge caffeine consumption. Instead, he looked at the levels of paraxanthine -- a relatively stable substance produced as the body metabolizes caffeine -- in blood samples from 487 women who had miscarried, and compared them with blood samples from 2,087 women who had not. The samples had been taken as part of the Collaborative Perinatal Project, a nationwide study of pregnancy, labor and child development between 1959 and 1966. Blood samples had been taken at two-month intervals during the pregnancy, at delivery and six weeks after delivery.

Researchers adjusted the results for age, smoking status and race or ethnicity, and found no increased risk of miscarriage for women who had paraxanthine levels up to 1,845 nanograms per milliliter -- which corresponds to about five cups of coffee per day. But for women with higher levels of paraxanthine, the risk doubled.

"Those levels were very, very high," Klebanoff said. "People used to drink more coffee 35 years ago, but even back then that was high."

For some experts, the new findings are part of a growing body of evidence that caffeine is not as dangerous as once believed. In 1980 the U.S. Food and Drug Administration advised pregnant women to avoid or limit their caffeine intake, after very high doses of caffeine were linked to birth defects in rats.

"That FDA advisory is one of my all-time pet peeves," said Michael Greene, M.D., director of maternal fetal medicine at Massachusetts General Hospital and associate professor of obstetrics and gynecology at Harvard Medical School. The rats in the study were given the equivalent of 70 cups of coffee a day, he said, which is not comparable with normal human consumption.

Greene acknowledges that other studies on women have found three to four cups of coffee a day may increase the risk of miscarriage during the first 12 weeks of a pregnancy. But he believes those miscarriages may have been the result of abnormal pregnancies rather than caffeine consumption.

The new findings don't necessarily mean pregnant women should consume more coffee. "'If you use caffeine, use it in moderation' is the advice usually given now," says Edee Hogan, R.D., spokeswoman for the American Dietetic Association. "If you choose not to have any, it's not going to hurt or help."

Others aren't ready to give caffeine the all-clear during pregnancy, even in moderate amounts. "I hold that the FDA advisory is still appropriate," says Brenda Eskenazi, Ph.D., professor of maternal and child health and director of Children's Environmental Health Resources at the University of California, Berkeley, School of Public Health. "This is an excellent study, but it only measures one outcome."

In an editorial published alongside the new study, Eskenazi cited studies where moderate amounts of caffeine were associated with changes in fetal heart rate and breathing patterns.

"I raised the issue of the neurodevelopment of the offspring," Eskenazi says. "If I were pregnant, I would be consuming less than one to two cups a day. Why take the risk? You can't just take one study as the be-all and end-all."

Klebanoff himself acknowledges his study won't end the dispute. "It's not over till it's over," he said. "I'm not sure there's any one paper that will ever resolve the debate."

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RELATED SITES:

National Institute of Environmental Health Sciences: Caffeine and pregnancy
The National Institute of Child Health and Human Development
U.S. Food and Drug Administration

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