There is no evidence that drinking moderate amounts of caffeine during pregnancy leads to premature births or underweight babies, a trial suggests.

Previous research has shown conflicting results on how caffeine intake during pregnancy affects fetal growth. Those studies mostly relied on women to remember how much caffeine they consumed while pregnant.

Danish researcher Bodil Hammer Bech, now chair of epidemiology at the University of California Los Angeles, designed an experiment to monitor 1,207 women who were less than 20 weeks pregnant. The women were randomly assigned to drink coffee with or without caffeine.

Participants did not know if they were drinking decaf or not. They were interviewed regularly about their caffeine intake from other drinks, such as tea and cola. Information about the length of gestation and baby's weight was collected at the end of the pregnancy.

There was no real difference in either the length of pregnancy or birth weight between the team groups, the researchers report in Friday's online issue of the British Medical Journal.

"A moderate reduction in caffeine intake in the second half of pregnancy has no effect on birth weight or length of gestation," they concluded.

Average caffeine intake was 182 milligrams lower among the decaffeinated group.

The researchers took into consideration the length of gestation, age, pre-pregnancy weight, and smoking status of the participants.

The study did not look at the effects of caffeine on other risks, such as miscarriage. It also did not compare the results to women who drank no coffee.