CAFFEINE consumption by pregnant women can significantly increase the risk of miscarriage, research shows.

The study of more than 1000 pregnant Californian women provides the most convincing evidence to date of such a link, the researchers said.

Research previously indicated an increased risk, but scientists were unsure whether those findings were affected by the fact that women having morning sickness might be less likely to drink caffeinated drinks, such as coffee, and less likely to have miscarriages.

"The relationship between caffeine intake and miscarriage was controversial," said De-Kun Li, a reproductive and peri-natal epidemiologist at Kaiser Permanente in Oakland, California, who led the study. "The question has been whether this association is really due to caffeine itself or something else."

To answer that, Dr Li and his colleagues studied 1063 women in the San Francisco area early in their pregnancies. They questioned the women about their beverage consumption and whether they were experiencing morning sickness.

Those women who consumed 200 milligrams of caffeine or more a day were about twice as likely to miscarry, the researchers reported on the website of the American Journal of Obstetrics and Gynaecology. That is about the amount of caffeine in two cups of coffee, five cans of soft drink or six cups of tea, Dr Li said.

The findings were consistent with earlier studies that had found an increased risk of miscarriage from daily caffeine consumption of about 150 to 300 milligrams, Dr Li said.

"But we went one step further in determining whether it was the caffeine itself or it was women changing their drinking pattern," he said. "My hope is our study will remove that uncertainty."

Based on the findings, Dr Li recommended women who are pregnant or trying to get pregnant minimise caffeine intake.

Tracy Flanagan, the director of women's health at Kaiser Permanente, agreed. "Avoiding [caffeine] may be even better. Consider switching to decaffeinated coffee and other decaffeinated beverages …" she said. "Learn to perk up instead with natural energy boosts, like a brisk walk, yoga stretches, snacking on dried fruits and nuts."

The Washington Post