One of the most rigorous studies ever to examine the issue found no link between moderate caffeine consumption late in pregnancy and either preterm delivery or low birth weight.
The Danish study compared pregnancy outcomes among women who mainly drank decaffeinated instant coffee during the second half of their pregnancy and those who drank at least three cups of caffeinated instant coffee a day.
No significant differences were seen in gestation times or birth weights among babies born to the two groups.
"I think we can say that moderate caffeine intake does not impact birth weight or pregnancy length," lead researcher Bodil Hammer Bech, MD, PhD, tells WebMD.
However, the study did not address the safety of caffeine consumption during the early months of pregnancy or the impact of consuming very large amounts of caffeine.
An earlier study from the same Danish research group suggested a link between very high coffee consumption and stillbirth.
"It would be reasonable to advise pregnant women to drink no more than three cups of coffee a day due to the fact that high (caffeine) intake may increase the risk of fetal death," Bech says.
No Major Differences
The Danish investigation looked at 1,200 healthy pregnant women who reported drinking at least three cups of caffeinated coffee a day, and who were less than 20 weeks pregnant when they entered the study.
The women were divided into two groups, with one group drinking mostly caffeinated instant coffee and the other group drinking instant decaffeinated coffee.
The women didn't know what kind of coffee they were given by the researchers.
Also, they were not advised to avoid intake of other caffeinated items -- such as tea, chocolate, cola, or other coffee. However, caffeine intake from these and other food and beverage sources was monitored closely.
The researchers adjusted for other risk factors for poor pregnancy outcome, including the mother's age, weight, and smoking status.
The average daily intake of caffeine for women who drank mostly decaffeinated coffee was 117 milligrams a day -- roughly the amount of caffeine found in three 12-ounce soft drinks.
Women in the caffeinated-coffee group ended up consuming about 317 milligrams of caffeine a day -- the equivalent of four cups of instant caffeinated coffee, or two and a half cups of brewed coffee.
Caffeine vs. Decaf
The average birth weight of babies born to the women in the lower caffeine group was 7.75 pounds, compared to 7.8 pounds for babies born to women who consumed more caffeine.
In the caffeinated group, 4.2% of infants were born prematurely and 4.5% were small for their gestational age, vs. a premature and underweight birth rate of 5.2% and 4.7%, respectively, in the decaffeinated group.
None of those differences reached statistical significance, meaning the differences could have been due to chance.
The Danish group's findings appear in the Jan. 26 issue of BMJ Online.
While the researchers found no evidence that caffeine influences outcomes late in pregnancy, concerns about its impact early in pregnancy and even before conception remain.
Drinking five or more cups of coffee a day was found to double a pregnant woman's risk of having a miscarriage in a Swedish study reported in 2000. There have also been suggestions that caffeine can lower fertility.
The March of Dimes, a group that works to prevent birth defects, recommends that pregnant women drink no more than two 8-ounce cups of coffee a day, and that they watch their intake of caffeinated tea, colas, and chocolate.
March of Dimes Deputy Medical Director Diane Ashton, MD, MPH, says pregnant women should limit their caffeine consumption as much as possible.
"If you can avoid caffeine altogether, hat is probably ideal," she tells WebMD.
"One or two cups of coffee a day probably won't pose a problem for most women," Ashton says. "But a woman who has had recurrent pregnancy losses or who is having problems becoming pregnant might want to consider a caffeine-free diet."
SOURCES: Bech, B. BMJ Online First, Jan. 26, 2007; online edition. Bodil Hammer Bech, MD, PhD, Institute of Public Health, department of epidemiology, University of Aarhus, Aarhus, Denmark. Diane Ashton, MD, MPH, deputy medical director, March of Dimes. The New York Times: "Study Links Use of Caffeine to Higher Risk of Miscarriage." WebMD Medical News: "Too Much Coffee Risky During Pregnancy." March of Dimes web site.
By Salynn Boyles
Reviewed by Louise Chang