Pregnant women who drink a few cups of coffee a day are not at increased risk of premature birth or having a low-birth-weight baby, scientists report.
Previous research showed that caffeine stays in the system longer in pregnant women and passes easily to the growing baby, who cannot readily metabolise it.
Health officials also warned that a high caffeine intake could affect birth weight, prematurity or the chance of having a miscarriage. But now Danish researchers say they have found no evidence of a link between drinking moderate amounts of caffeine and pregnancy outcome.
They recruited more than 1,000 women before they were 20-weeks pregnant, who drank at least three cups of coffee a day. The group was split into two, with 568 women drinking caffeinated instant coffee for the duration and 629 women drinking decaffeinated instant coffee.
Each woman was regularly monitored to check their caffeine intake, including from other drinks such as tea and cola. The authors then monitored the birth weight of 1,150 newborn babies and the length of pregnancy for 1,153 of the babies.
The study, published online by the British Medical Journal (BMJ), concludes: "No significant differences were found for mean birth weight or mean length of gestation between women in the decaffeinated coffee group (whose mean caffeine intake was 182mg lower than that of the other group) and women in the caffeinated coffee group."
The authors conclude that a moderate reduction in caffeine intake in the second half of pregnancy in these women had "no effect" on birth weight or length of pregnancy.
The women were not told what type of coffee they were drinking, and the research was adjusted to take into account factors such as age, pre-pregnancy weight and whether the women smoked.
When the adjustments were made, the average weight of babies born to women in the decaffeinated group was "16g higher than those born to women in the caffeinated group", the study said. The average difference in the length of pregnancy was less than two days between the two groups.
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In the caffeinated group, 4.2% of infants were regarded as born prematurely while 4.5% were underweight, compared to 5.2% premature births and 4.7% underweight babies in the decaffeinated group. The authors, from the University of Aarhus, do not regard any of these differences as statistically significant.
