LONDON (AP) _ Pregnant women who drink eight or more cups of coffee a day could double their risk of stillbirth compared with pregnant women who do not drink coffee, new research suggests.
However, experts cautioned that the findings, published this week in the British Medical Journal, were tenuous and several factors other than coffee could explain the results.
Previous studies have linked the consumption of more than three or four cups of coffee a day with miscarriage and low birth weight.
``Women should not be worried because this study has serious limitations,'' said Lisa Signorello, an epidemiologist at the International Epidemiology Institute in Rockville, Md., and an assistant professor of medicine at Vanderbilt University in Nashville, Tenn.
Stillbirths are rare, occurring in less than 1 percent of pregnancies. The findings in this Danish study are based on 11 stillbirths among 950 women drinking eight or more cups of coffee a day, and scientists do not like to draw firm conclusions from numbers that low.
The study, conducted by scientists at Aarhus University, involved 18,478 pregnant women attending the obstetrics department at the university hospital between 1989 and 1996.
One in 250 pregnancies ended in stillbirth among women who drank no coffee during their pregnancy.
But three in 250 pregnancies ended in stillbirth among the 950 women who drank more than eight cups daily. That is a tripling of the risk.
However, that risk dropped to double when researchers accounted for the women's smoking and drinking habits, age, and other factors known to influence pregnancy success.
There was no increased chance of stillbirth among the pregnant women drinking less than eight cups of coffee a day.
``Women who have such a high intake of coffee also come with a set of other characteristics _ like they are more likely to smoke, they have a higher intake of alcohol, they are older, they've had more pregnancies, they've had fewer years of education,'' Signorello said.
``All of these things have been shown to be risk factors for pregnancy problems.''
The study's authors acknowledge their results may not prove a real coffee effect and say further research is needed.
Another caveat is that coffee intake was measured only once _ at 16 weeks of pregnancy _ and coffee consumption is known to change during pregnancy.
Alan Leviton, a professor of Neurology at Harvard Medical School and Children's Hospital in Boston, said there could be another explanation _ something called the pregnancy signal theory.
``All the recent studies show that women tend to reduce their coffee consumption about four to six weeks into pregnancy, even if they weren't planning to. All of a sudden, they don't want as much coffee,'' Leviton said.
It seems they become averse to the smell.
``This is associated with elevated hormones, or signals, that the placenta is making. The inference is that the healthier the placenta, the stronger the pregnancy signal,'' Leviton said.
``The woman who does not have a good implantation of her placenta doesn't make as many hormones, which puts her at risk of pregnancy problems such as stillbirth.''
The pregnancy signal theory would contend that the ability to consume as much coffee as before pregnancy is an indication that the pregnancy already is not going well.