New studies, different outcomes on caffeine, pregnancy

One study found that consuming 200 milligrams or more of caffeine per day doubled the risk of miscarriage.

USA TODAY
Most women know they shouldn't smoke or drink alcohol while pregnant. But what about caffeine?

Two new studies reach somewhat different conclusions about the connection between drinking caffeine and miscarriage risk, an inconsistency that dates back to the 1980s, when scientists began investigating the subject.

It's plausible that caffeine could trigger a miscarriage, a pregnancy loss before 20 weeks gestation. Caffeine crosses the placenta, but a fetus is not able to metabolize it. Caffeine might adversely affect cell development in the fetus and decrease blood flow in the placenta.

But some scientists have speculated that caffeine only appears to increase miscarriage risk because women with morning sickness, who are more likely to carry a pregnancy to term, avoid coffee and other drinks that contain it.

In both of the new studies, the authors say they took morning sickness into account, so their findings relate to caffeine and not to other characteristics of pregnant women who drink it.

In one study, in the American Journal of Obstetrics & Gynecology, Kaiser Permanente researchers analyzed information about caffeine drinking by 1,063 women early in their pregnancies.

Women who reported drinking less than 200 milligrams of caffeine per day (about two cups of regular coffee or five cans of caffeinated soda) were 40% more likely to miscarry than women who said they drank no caffeinated beverages. Those who drank 200 milligrams or more of caffeine per day had about twice the miscarriage risk as women who drank none.

"My suggestion is women who are pregnant and women who are trying to become pregnant should consider stopping caffeine entirely," co-author De-Kun Li says. If you must have that morning cup of coffee, he says, let it be your only one of the day.

Not so fast, says David Savitz, lead author of the other new study on the subject, in the January issue of Epidemiology. Savitz, a professor in community and preventive medicine at New York's Mount Sinai School of Medicine, found no link between miscarriage and caffeine consumption in the 2,407 pregnant women he studied.

Compared with women in other studies, though, Savitz says, his subjects were pretty light caffeine drinkers. The biggest consumers drank the equivalent of only about two cups of coffee a day, he says.

"It's really hard as a physician to translate this into clinical practice," says OB-GYN Tracy Flanagan, women's health director at Kaiser Permanente Northern California, who wasn't involved with Li's study. Flanagan advises pregnant women in their first trimester to limit their caffeine to two cups of coffee or five cans of soda a day. Better yet, she says, switch to decaffeinated beverages.

"Here is something that women can actively do" to reduce their miscarriage risk, Flanagan says.

After her first pregnancy ended in a miscarriage, self-described caffeine addict Tammy Plotkin-Oren of El Cerrito, Calif., swore off the stuff. Her sister, an OB-GYN, told her: "Is it going to ensure that you're not going to have another miscarriage? No." Coincidence or not, Plotkin-Oren, 35, went on to deliver three healthy daughters.