Researchers in the U.S. say they have found strong evidence that high doses of caffeine during pregnancy significantly increase the risk of miscarriage.
They say pregnant women who drink two or more cups of coffee a day double their risk of having a miscarriage compared to those who avoid caffeine.
The researchers from Kaiser Permanente Division of Research conducted a study which they say proves that 200 milligrams or more per day or the equivalent of two cups of coffee, significantly increases the risk of a miscarriage.
The study involved 1,063 pregnant women who were members of the Kaiser Permanente health plan in San Francisco from October 1996 through October 1998 who did not change their caffeine consumption during pregnancy.
The researchers say they found that women who consumed the equivalent of two or more cups of regular coffee or five 12-ounce cans of caffeinated soda were twice as likely to miscarry as pregnant women who avoided caffeine.
They say this risk appeared to be related to the caffeine, rather than other chemicals in coffee, because they also saw an increased risk when the caffeine was consumed in soda, tea, and hot chocolate.
Lead researcher Dr. De-Kun Li says a number of studies have found a link between caffeine use during pregnancy and miscarriage.
Dr. Li says many researchers suspect caffeine is harmful because it stresses the immature metabolism of the fetus and also decreases the blood flow in the placenta, which could harm the fetus.
The researchers say their study may finally resolve conflicting reports about the link between caffeine consumption and miscarriage.
Dr. Li a perinatal epidemiologist, says the safe dose is zero and if pregnant women must drink coffee they should try to limit it to one cup or at the most two cups or better still switch to decaffeinated beverages.
Caffeine occurs naturally in a range of foods, such as coffee, tea and chocolate, and is added to some soft drinks and is also used in cold remedies and antihistamines to counter the drowsy effects of other ingredients.
Caffeine raises the heart rate and metabolism and is also a diuretic that causes the body to lose water, other fluids and calcium.
The study appears in the American Journal of Obstetrics and Gynecology.