The study showed that women who consumed an average of five or more drinks per sitting were more than twice as likely than non-drinkers to have an infant with either of the two major infant oral clefts: cleft lip with or without cleft palate, or cleft palate alone.
Women who drank at this level on three or more occasions during the first trimester were three times as likely to have infants born with oral clefts.
"These findings reinforce the fact that women should not drink alcohol during pregnancy," said Lisa A. DeRoo, Ph.D., an epidemiologist at NIEHS and author on the study.
"Prenatal exposure to alcohol, especially excessive amounts at one time, can adversely affect the foetus and may increase the risk of infant clefts," she added.
The causes of clefts are largely unknown, but both genetic predisposition and environmental factors are believed to play a role in their development.
The study included 573 mothers who had babies born with cleft lip with or without cleft palate and cleft palate only; as well as 763 mothers randomly selected from all live births in Norway. The average age of the mostly married mothers was 29 years.
Mothers completed a self-administered mailed questionnaire focused heavily on the mother's lifestyle and environmental exposures during her first three months of pregnancy when a baby's facial development takes place.
The researchers found increased risks of orofacial clefts among infants whose mothers reported binge-level drinking of an average of five or more drinks per occasion during the first-trimester compared to non-drinkers.
Risk was further increased among women who drank at this level most frequently.
Both animal and human data suggest that it is the dose of alcohol consumed at one time during pregnancy rather than the frequency or total amount over time that matters most.
"The greater the blood alcohol concentration, the longer the foetus is exposed. A single binge during a critical period of an infant's development can be harmful," said DeRoo.
The study appears online today as an advance access publication in the American Journal of Epidemiology.