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Women who binge-drink early in pregnancy may raise their risk of having a baby with an oral cleft, a new study shows.

Oral clefts, including cleft lip and cleft palate, are among the most common type of birth defect. They arise when the tissues that form the roof of the mouth and the upper lip fail to fuse properly, sometime between the fifth and ninth week of pregnancy.

The causes of oral clefts are not entirely clear, but a combination of genetic predisposition and environmental factors seems to be at work. Some earlier studies have linked drinking during early pregnancy to an increased risk of this birth defect.

These latest findings suggest that the amount a woman drinks at any one time may be especially important, according to the researchers.

Lead investigator Dr. Lisa A. DeRoo, of the National Institute of Environmental Health Sciences (NIEHS), Durham, North Carolina, and colleagues, evaluated 1,336 Norwegian women who gave birth between 1996 and 2002.

Women binged in the first trimester were twice as likely to have a baby with a cleft lip, cleft palate or both.

The risk was tripled among women who had binged three or more times in the first trimester, the researchers report in the American Journal of Epidemiology.

Norway has one of the highest rates of oral clefts in Europe. In addition, weekend binge drinking is fairly common in Norway as well as other Nordic countries.

"Prenatal exposure to alcohol, especially excessive amounts at one time, can adversely affect the fetus and may increase the risk of infant clefts," DeRoo said in a statement released by the NIEHS.

Bingeing may be particularly harmful to the fetus, she and her colleagues note, because it results in a high concentration of alcohol in the blood at one time. The time window for lip and palate development in the embryo is brief, and even a single binge during this time could be dangerous, the researchers add.

"These findings reinforce the fact that women should not drink alcohol during pregnancy," DeRoo said.

Fortunately, few women do drink heavily during pregnancy, according to Dr. Allen J. Wilcox, an NIEHS researcher who also worked on the study.

"But," he said in the agency statement, "the fact that it is happening at all tells us we need to do a better job of letting mothers know about the effects that alcohol can have on their baby's development."

SOURCE: American Journal of Epidemiology, online July 31, 2008.