New research suggests drinking more than a few cups of coffee or other caffeinated beverages a day may increase a pregnant woman's miscarriage risk.
According to the study, women 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.
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.
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.
Most Miscarriages Unavoidable
"The fact is, the vast majority of pregnancies that miscarry do so because of chromosomal abnormalities," she says. "From a clinician's standpoint, it is nice to be able to tell a patient that limiting caffeine just may positively impact their pregnancy."