Pregnant women have long been told to limit the amount of caffeine they consume. Now a new study shows caffeine may dramatically increase the chance of miscarriage. VOA's Carol Pearson has more.

A new study shows that pregnant women who drink a cup and a half of coffee a day -- or more than 200 milligrams of caffeine -- double their risk of having a miscarriage.

And the warning goes for tea, caffeinated soft drinks and even some medications.

One of the screening questions asked of pregnant women is, "During this pregnancy, have you been drinking coffee at all?"

"What's different about this study is that it shows that a fairly low level of caffeine may be associated with miscarriage. And that's important," says Dr. Tracy Flanagan, who specializes in obstetrics and gynecology.

The research shows those who consumed less than 200 milligrams of caffeine per day still appeared to increase their risk of miscarriage.

No one knows precisely why caffeine appears to have this effect, but experts say it may increase a fetus's heart rate, or restrict blood flow to the baby.

The study was conducted by Kaiser Permanente's Division of Research*, and prompted the March of Dimes, a leader in infant and maternal health, to revise its recommendations on caffeine intake for pregnant women.

At least one expert says most miscarriages result from abnormalities in the fetus.

But the study's author says pregnant women should try to give up caffeine for at least the first three or four months of pregnancy.

* Correction issued 30 Jan 08