Study Links Caffeine to Miscarriage

Jan. 22, 2008 -- Drinking more than a few cups of coffee or other caffeinated beverages a day may increase a pregnant woman's miscarriage risk, new research suggests.

Women in the study who consumed more than 200 mg of caffeine a day -- the amount found in about two 8-ounce cups of regular-strength coffee -- had twice the risk of miscarriage as pregnant women who consumed no caffeine.

Researchers say the study offers some of the strongest evidence to date linking caffeine and miscarriage. But an expert who spoke to WebMD disagrees, saying the jury is still very much out on the issue.

"The evidence just isn't there to say that caffeine is a risk factor for miscarriage," says epidemiologist Lisa B. Signorello, ScD, who has studied caffeine and miscarriage. "This is a very difficult thing to investigate, and there is simply no gold-standard study that answers the question."

Caffeine and Miscarriage

The new study included 1,063 women followed from early in their pregnancies until up to 20 weeks of gestation by researchers from the Kaiser Permanente Division of Research.

The women were interviewed at study entry about their caffeine consumption and other factors known to be risk factors for miscarriage.

A total of 631 women (79%) reported reducing their caffeine consumption after becoming pregnant, while 152 (19%) said they did not change their habits.

Overall, 172 women (16%) in the study ended up having miscarriages. According to the March of Dimes, about 15% of diagnosed pregnancies end in miscarriage.

The researchers concluded that consuming more than 200 mg of caffeine a day doubled the risk of miscarriage, compared with consuming no caffeine at all.

Researchers cited their attempt to control for the confounding effect of caffeine aversion during pregnancy as a major strength of the study.

Early-pregnancy nausea and vomiting has been linked to lower miscarriage risk, according to the researchers. Nausea and vomiting may also contribute to caffeine aversion.

So women who are more likely to have a miscarriage might also be more likely to continue drinking coffee, and this could explain the link between caffeine and miscarriage seen in earlier studies.

But Signorello says there were not enough women in the study who did not change their caffeine consumption to conclude that caffeine was a risk factor in the miscarriage.

And the women who consumed the most caffeine were also more likely to have other risk factors for miscarriage, including being over 35 years old, having a history of miscarriage, having no morning sickness symptoms, and smoking and drinking alcohol.

Signorello is a researcher and epidemiologist with the Vanderbilt-Ingram Cancer Center and the International Epidemiology Institute in Rockville, Md.

"These women were very different from people who didn't consume caffeine, and they were different in all the ways that are associated with miscarriage," she tells WebMD.