Pregnant women who smoke or regularly breathe second-hand smoke are twice as likely to have a baby with a cleft lip than nonsmokers. Cleft lip and cleft palate are common birth defects, arising when the tissues that form the roof of the mouth and the upper lip do not fuse properly, sometimes between the fifth and ninth week of pregnancy. To investigate the association between smoking by pregnant women and risk of oral clefts among their children, Norwegian researchers assessed 1,336 infants, 573 of whom had an oral cleft. The mothers were asked to complete a questionnaire four months after birth of the baby and DNA was collected from parents and children, and assayed for genes related to detoxification of compounds of cigarette smoke. It was found that women who smoked more than 10 cigarettes per day during their first trimester were nearly twice as likely to have a baby with a cleft lip as nonsmokers. Also, nonsmoking women who were near a smoker for at least two hours each day had a 60 percent higher risk than women who were not exposed to passive smoking. There was no association found between parental genes and the increased or decreased risk of cleft lip among children. The findings substantiate previous studies that have linked mothers' smoking to cleft lip and, less consistently, to cleft palate, and also suggest that smoking affects the odds of cleft lip regardless of certain genes.
Epidemiology
July 2008