Study of Caffeine and Miscarriage Yields Surprise Finding About Decaf

To drink or not to drink coffee? That is a question pregnant women have pondered since 1980 when the Food and Drug Administration issued a warning, based on animal studies, to avoid or restrict caffeine intake during pregnancy.

The concern is that caffeine metabolizes more slowly during pregnancy, so caffeine blood levels remain high, even if consumption is decreased. Caffeine is rapidly absorbed from the digestive tract, distributes through all body tissues, and easily crosses the placenta. Animal studies have linked caffeine to increased rates of birth defects, low birth weight, stillbirths and miscarriage.

But a new study of 5,144 pregnant women by scientists at the State Department of Health, Kaiser Permanente Division of Research and UCSF has turned up some surprising results. The study found no significant increased risk for spontaneous abortion, or miscarriage, associated with caffeine consumption. Even among women considered heavy caffeine consumers (300 milligrams or three cups of coffee a day) miscarriage risk increased only slightly -- about 1.3 times the risk as noncaffeine users, according to the study in the September issue of the journal Epidemiology.

The study, however, found that women who drank three or more cups of decaffeinated coffee a day in the first trimester had 2.4 times the risk of miscarriage as those who did not drink decaf.

Researchers, however, are not urging pregnant women to pull the plug on decaf. The connection between miscarriage and decaffeinated coffee is more likely an “epidemiologic phenomenon,” says UCSF addiction expert and pharmacologist Neal Benowitz, MD, whose laboratory at SFGH conducts studies on caffeine metabolism.

“We suspect that the apparent risk associated with heavy decaffeinated coffee intake resulted from women with nonviable pregnancies experiencing fewer symptoms of pregnancy and consequently consuming more decaffeinated coffee,” the researchers said.

If a woman inher first trimester, for example, stopped feeling nauseous -- a potential sign that the pregnancy is in trouble -- she may be more likely to drink more coffee than a woman with morning sickness. Early in pregnancy, says Benowitz, women might be more motivated to substitute decaf for regular coffee because of concerns for the safety of the fetus.

Among the heavy decaffeinated coffee drinkers (three or more cups daily), the spontaneous abortion rate was 18.5% for the 27 women who had increased their consumption, 33.3% for the six women who had reduced to three cups per day, and 24% for the 25 women who had not changed their consumption since before pregnancy, reported lead author Laura Fenster of the Department of Health Services in Emeryville, California. The overall miscarriage rate for the women in the study was 9.7%.

The researchers could not link any chemicals in decaffeinated coffee or the process of removing caffeine to miscarriage risks.

By Andy Evangelista