Does Caffeine Cause  Miscarriage?

[January 2008] A new study reinforces the theory that high daily doses of caffeine consumed during pregnancy can be harmful. Study results showed that high caffeine intake may double the risk of miscarriage.

Apparently, it makes no difference if the caffeine comes from coffee, tea, soda, or hot chocolate. What is important is the amount - the study found that when women drink more than 200 milligrams (mg) of caffeine daily (around two or more cups of coffee), the risk of miscarriage increases twofold.

Women who consumed less than 200 mg of caffeine daily had a more than 40 percent chance of miscarriage. But this level of risk is not significant statistically.

"What we found was that if women have heavy caffeine intake - greater than 200 milligrams a day - they have double the risk of miscarriage than women that don't have any caffeine," says lead author and investigator, Dr. De-Kun Li who works in the Kaiser Permanente Division of Research in Oakland, California.

Results of the study were published in a recent issue of the American Journal of Obstetrics and Gynecology.

Research Controlled for Morning Sickness

While previous research has demonstrated a link between caffeine consumption and miscarriage, this is the first study to thoroughly control for morning sickness, which typically causes many women to avoid caffeine, explains Dr. Li.

“This study strengthens the association between caffeine and miscarriage risk because it removes speculation that the association was due to reduced caffeine intake by healthy pregnant women,” Dr. Li says.

In addition to caffeine intake, the researchers also accounted for other known risk factors for miscarriage, such as smoking, a history of previous miscarriage, alcohol use, and more.

"If you have a low risk of miscarriage, the effect of caffeine tends to show more," says Dr. Li.

Why is Caffeine Harmful?

Researchers have suspected for several years that caffeine may harm the fetus. Caffeine crosses through the placenta to the fetus, but it can be hard for the fetus to metabolize. Caffeine may also change cell development and lower placental blood flow, which may then cause a negative effect on the baby's development.

The study included 1,063 pregnant women who received their care from Kaiser Permanente Medical Care Program in San Francisco.

The women were interviewed about their caffeine intake about 10 weeks into their pregnancy. Overall, around 16 percent of the pregnant women miscarried. Around 25 percent of the women who miscarried reported consuming no caffeine during their pregnancy.

Sixty percent stated they had up to 200 mg of caffeine daily (also equal to five 12-ounce cans of caffeinated soda). Fifteen percent consumed more than 200 mg of caffeine every day.

The increased risk of miscarriage appeared to be due to the caffeine itself, rather than other possible chemicals in coffee. This appears to be true because caffeine intake from non-coffee sources such as caffeinated soda, tea, and hot chocolate also showed an increased risk of miscarriage.

Some Doctors Are Unsure About Link, But Agree About the Limit

"Women shouldn't drink more than two regular cups of coffee a day, and hopefully they stop drinking totally for at least the first three months. It's not a permanent stop. If they really have to drink, limit the amount to one or two cups - a regular cup is about seven and half ounces," Dr. Li explains.

However, not all doctors agree that there is a direct cause-and-effect relationship between caffeine and miscarriage.

"The problem with this study is that when people miscarry, a large percentage of those miscarriages are due to genetic abnormalities, and the researchers didn't say whether these were normal or abnormal fetuses," says Dr. Laura Corio, an obstetrician and gynecologist at Mount Sinai Medical Center in New York City.

"Women are always worrying and wondering, 'What did I do?' Before we say a woman drank too much caffeine and that's why she had a miscarriage, let's see if it was an abnormal or normal pregnancy," says Dr. Corio.

"I think about 60 to 80 percent of miscarriages are due to genetic abnormalities," she adds.

In another recent study published in Epidemiology, Dr. David Savitz found results that were inconsistent with Dr. Li's results. In the study, 2,407 pregnant women and their caffeine consumption were evaluated in relationship to their pregnancy loss.

Dr. Savitz, a professor in community and preventive medicine at New York's Mount Sinai School of Medicine, concludes that there is little indication of possible harmful effects of coffee and caffeine consumption. Reported miscarriage at the time of the interview was related to an increased risk among those with a previous loss in their pregnancy history.

Regardless, Dr. Corio advises her pregnant patients to limit their caffeine intake. "Women have a responsibility to the fetus - no cigarettes, no alcohol, and just one cup of coffee a day," she says, noting that many store-bought cups of coffee contain even more caffeine than a cup from home. So, a woman must be aware of how much caffeine is in her favorite coffee.

"Have less than 200 milligrams a day, no matter what the source - coffee, tea, cola, or chocolate," Dr. Corio advises. She says caffeine has also been linked to low birth weights and smaller head circumferences.

Dr. Li also recommends limiting caffeine to less than 200 mg a day, especially in the early months of pregnancy and in the preconception period, if possible.

Unsure about how to get an energy boost without caffeine? Consider other ways to raise your energy level, such as taking a walk, yoga stretches, or snacking on dried fruits or nuts.

Always consult your physician for more information.