Researchers say they have stronger evidence that pregnant women should fight the urge to get regular jolts from caffeinated coffee, tea, soft drinks or hot chocolate.
Since the 1980s, several studies have cited evidence that caffeine consumption during pregnancy increased the risk of miscarriage, a common complication in the first few months of pregnancy.
Dr. De-Kun Li, a perinatal epidemiologist with the Kaiser Permanente Division of Research, said some experts challenged the methodology of those studies, charging that they failed to account for contributing factors such as smoking, alcohol use and pregnancy-related symptoms.
Li was the lead investigator for research published today in the online issue of the American Journal of Obstetrics and Gynecology. He said the recent Kaiser study controlled for those factors and still found that high doses of caffeine increased the miscarriage risk.
The women in the Kaiser study who consumed the most caffeine -- 200 milligrams or more per day -- had twice the miscarriage risk as women who abstained from the stimulant. That amount of caffeine is found in two or more cups of coffee or five 12-ounce cans of caffeinated soda.
The increased risk appeared to be linked to the caffeine, rather than other chemicals in coffee, the study said. The risk of miscarriage was similar among women who consumed caffeine from soft drinks, tea and hot chocolate.
"The main message for pregnant women is that they probably should consider stopping caffeine consumption during pregnancy," Li said.
Women who are trying to get pregnant should consider heeding the advice, he said, because of the miscarriage risk in early pregnancy.
Kaiser officials said the study results will be shared with doctors providing prenatal care at its medical offices in the Bay Area, Stockton, Manteca and the Modesto area.
The researchers examined the caffeine use and pregnancy outcomes of 1,063 Kaiser Permanente members in the Bay Area. Sixteen percent of the women had miscarriages.
Of the 164 women who reported consuming more than 200 milligrams of caffeine per day, the miscarriage rate was 25 percent, the study says. The 264 women who consumed no caffeine had a 12 percent miscarriage risk.
Most women in the study reported consuming less than 200 milligrams of caffeine per day. The miscarriage rate among those women was 15 percent.
Fetus can't handle caffeine
Medical experts suspect that caffeine can be harmful because it passes through the placenta to the fetus. The metabolic system of the fetus is not mature enough to break down the chemical.
Caffeine can disrupt the sleep of the mother and fetus, and some research has linked heavy caffeine use with low birth weights.
The women in the Kaiser study were interviewed from 1996 to 1998, and researchers tracked the outcomes of their pregnancies by reviewing medical records or making personal contacts.
Li said it took several years to publish the results on caffeine consumption, because researchers were working on other studies using the same study group.
Some experts took issue with previous studies for failing to recognize that women who are healthy during pregnancy often suffer from nausea and vomiting, and that creates an aversion to caffeine.
According to this argument, the group of women in the studies who had less caffeine intake and fewer miscarriages were more healthy than the women who didn't have the caffeine aversion.
Li said the Kaiser study controlled for this factor by evaluating the outcomes of women who never changed their caffeine consumption.
The worry is heavy consumption
Even though the study found an increased miscarriage risk from consuming small amounts of caffeine, medical experts are most concerned about heavy caffeine use during pregnancy.
"Women should not feel guilty if they had minimal doses of caffeine during their pregnancy," said Dr. David Walton, a Kaiser specialist who focuses on high-risk pregnancies. "With small amounts of caffeine intake, the statistical effects are pretty minimal."
Dr. Robert Altman, an obstetrician with Sutter Gould Medical Foundation in Modesto, said it's common to advise pregnant women to limit caffeine intake. He said solid research has associated caffeine consumption of 300 milligrams or more per day with miscarriage and restricted growth of the fetus.
"If the woman is a heavy caffeine user, we need to talk to her about coming off the caffeine," Altman said. "A single caffeine beverage, a cup of coffee or a Pepsi, normally is not associated with these problems."
Women who feel they need a pick-me-up should make sure to get enough rest, eat healthy and exercise daily. Walking and swimming are good activities during pregnancy and should give them energy, Altman said.
"If you definitely need caffeine to get you going, try keeping it to one cup or less a day," said Dr. Tracy Flanagan, director of women's health for Kaiser in Northern California. "Avoiding it may be even better. Consider switching to decaffeinated coffee and other decaffeinated beverages during your pregnancy."
Bee staff writer Ken Carlson can be reached at firstname.lastname@example.org or 578-2321.