"Compared with women who did not drink coffee, women who drank four to seven cups a day had an 80 percent increased risk of stillbirth, and women who drank eight or more cups a day had three times the risk," says Dr. Kirsten Wisborg, director of the perinatal epidemiological research unit at Aarhus University Hospital in Denmark, lead author of a paper reporting the finding in the Feb. 22 British Medical Journal.
It's the caffeine that does it, Wisborg says. Caffeine may tighten the arteries in the uterus so much that the fetus doesn't get enough oxygen, or it may cause abnormal, and eventually fatal, arrhythmias in the unborn heart.
It's true that women who drink a lot of coffee are more likely to smoke and drink a lot, Wisborg says. "However, adjusting for these factors changed the association between coffee and stillbirth only slightly," she says.
The study started in 1989, when pregnant women booked for delivery at the hospital were asked to give information about a number of habits, including consumption of coffee and other caffeine-containing drinks, smoking, and alcohol intake. By the time the study was finished, in 1996, the hospital's epidemiologists had records on more than 18,000 pregnancies.
The risk of stillbirth or death during the infant's first year of life was directly related to coffee intake, the study found. For example, there were 31 stillbirths among the 7,878 women who drank no coffee, a rate of 3.9 stillbirths per 1,000 deliveries. The 950 women who drank more than eight cups a day had 11 stillbirths, a rate of 11.6 per 1,000 deliveries.
The difference in the risk of first-year deaths was not so sharp, but it clearly existed: 9.6 per 1,000 births for women who had more than eight cups a day, a 4.3 per 1,000 births for women who drank no coffee.
Other studies have shown an association between caffeine intake and other pregnancy problems, such as low birth weight and spontaneous abortion, Wisborg notes. The new study adds significant evidence on the need to reduce that intake, she says.
"How to advise pregnant women or women planning to become pregnant is a very difficult question," Wisborg says. "Based on our knowledge today, it seems reasonable at least to reduce coffee intake during pregnancy to less than five cups per day."
"There has been concern for years about caffeine during pregnancy," says Dr. Edward F. Bell, director of neonatology at the University of Iowa, a spokesman for the American Academy of Pediatrics. But it's still uncertain where the line should be drawn, he says.
"Is three cups better than 10, is zero better than three?" he asks. "Most of the studies don't address that. Maybe someday we will have data about complete abstention, but we don't have that data now."
But, Bell says, "if it were my wife, I would settle for one or two cups a day."
You can get advice about caffeine and pregnancy from the March of Dimes Birth Defects Foundation.