In the past women were told to limit their caffeine intake, but new research is suggesting that pregnant women should avoid caffeine altogether.
Scientists now say drinking more than 200 milligrams of caffeine a day can double a woman's risk of miscarriage - that's the amount in a cup and a half of coffee.
Experts believe caffeine is difficult for the fetus to handle and can lower blood flow to the baby.
"What's different about this study is that it shows that, that a fairly low level of caffeine may be associated with miscarriage. And that's important," said Dr. Tracy Flanagan, director of Women's Health at Kaiser Permanente.
Doctors say women should try to avoid caffeine for at least the first three or four months of pregnancy.