Women who drink even moderate amounts of caffeine during pregnancy -- whether from coffee, tea, caffeinated soft drinks or hot chocolate -- have almost double the risk of miscarriage compared to women who stay away from such drinks.
The link between caffeine and the risk for miscarriage is not new. In fact, there have been more than a dozen studies on the issue in recent years.
But this new research, from the Kaiser Permanente Division of Research, is considered more definitive because it thoroughly controlled for morning sickness, the authors say.
Women who become nauseated by coffee early in pregnancy often choose to avoid it and therefore may have skewed the results of previous studies.
This study looked at 1,063 pregnant women in San Francisco from October 1996 through October 1998 who never changed their pattern of caffeine consumption during their pregnancy. They then looked to see how the women fared for the first 20 weeks of their pregnancies.
It found that women who consumed 200 mg or more of caffeine per day -- the amount in about two or more cups of regular coffee or five 12-ounce cans of caffeinated pop -- had twice the miscarriage risk as women who consumed no caffeine.
Among women who consumed no caffeine, the miscarriage rate was 12.5 per cent. In comparison, 25.5 per cent of women who consumed more than 200 mg of caffeine a day miscarried.
Even smaller amounts of caffeine seemed to increase the risk of miscarriage, found Dr. Tracy Flanagan, the director of Women's Health at Kaiser Permanente.
"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," she said Monday.
In didn't matter what the beverage was; once the 200 mg caffeine level was reached, the miscarriage rate increased, suggesting that caffeine itself is the culprit, rather than some other chemical in coffee.
The research appears in the current online issue of American Journal of Obstetrics and Gynecology.
Dr. De-Kun Li, the lead investigator of the study, says that this study should erase any doubt of the risks of caffeine in pregnancy.
"The main message for pregnant women from these findings is that they probably should consider stopping caffeine consumption during pregnancy because this research provides clearer and stronger evidence that high doses of caffeine intake during pregnancy can increase the risk of miscarriage," Li said in a statement.
It's not clear why caffeine can cause miscarriage. It's known that caffeine crosses through the placenta to the fetus and can be difficult for the fetus to metabolize because of the under-developed metabolic system.
Caffeine also may influence cell development and decrease placental blood flow, which may lead to an adverse effect on fetal development.
Dr. Gideon Koren of the Motherisk program at Toronto's Hospital for Sick Children says the new study blows what may be a small risk out of proportion. He says there is no actual proof the caffeine itself is causing any of the miscarriages. His research suggests small amounts are safe for mothers.
"Our advice is be moderate. Drink two to three cups a day, max," he says.
And what else can a fatigued mom-to-be do for her daily energy jolt?
"Learn to perk up instead with natural energy boosts like a brisk walk, yoga stretches, snacking on dried fruits and nuts," Flanagan suggests.
