Drinking too much coffee during pregnancy raises the risk of stillbirth, research suggests.
Diet is important during pregnancy
Scientists in Denmark found that pregnant women who drink eight or more cups of coffee a day run more than twice the risk of stillbirth compared with women who do not drink coffee.
The researchers focused on 18,478 pregnant women who booked for delivery at Aarhus University Hospital between 1989 and 1996.
The women completed two questionnaires, providing information such as medical history, smoking habits, alcohol and coffee consumption.
It seems reasonable at least to reduce coffee intake during pregnancy to less than five cups per day
The risk of stillbirth increased with the number of cups of coffee a day during pregnancy.
Compared with women who did not drink any coffee, women who drank four to seven cups a day had an 80% increased risk of stillbirth, and women who drank eight or more cups a day a 300% increased risk.
However, there was no association between coffee consumption and death in the first year of life.
Smokers and drinkers
The researchers admit that women who drink a lot of coffee are more likely to smoke, and to drink alcohol.
But even when these factors were taken into consideration coffee drinking still seemed to increase the risk of stillbirth.
Those who drank eight or more cups a day were at 220% increased risk compared with those who abstained.
The reason why coffee appears to increase the risk of stillbirth is unclear.
However, it is thought that caffeine may cause a tightening of the blood vessels that feed the placenta, leading to a reduced oxygen supply to the developing foetus.
Alternatively, caffeine may have a direct, damaging effect on the foetus's developing heart.
Lead researcher Dr Kirsten Wisborg, of Aarhus University Hospital, told BBC News Online: "How to advise pregnant women or women planning to become pregnant is a very difficult question.
"But based on our knowledge to day it seems reasonable at least to reduce coffee intake during pregnancy to less than five cups per day."
Roger Cook, of the British Coffee Association, says that pregnant women should not be alarmed by these results and should continue to enjoy their coffee in moderation.
He said: "The results of this study do not alter the advice given to pregnant women, on caffeine consumption during pregnancy, by the Food Standards Agency, which states that 300 mg caffeine - equivalent to three mugs or four cups of coffee per day - is perfectly safe and will have no adverse effect on the mother or the foetus.
"Further, the Centre for Pregnancy Nutrition, state that it is perfectly safe for a pregnant woman to drink up to four or five cups of coffee or tea a day while pregnant or breastfeeding."
The research is published in the British Medical Journal.