The independent role of prenatal and postnatal exposure to active and passive smoking on the development of early wheeze in children.

Maternal smokingduring pregnancyincreases childhood asthma risk, but health effects in children of nonsmoking mothers passivelyexposed to tobacco smokeduring pregnancyare unclear. We examined the association of maternal passive smokingduring pregnancyand wheezein children aged <= 2 years. Individual data of 27 993 mother-child pairs from 15 European birth cohorts were combined in pooled analyses taking into consideration potential confounders. Children with maternal exposureto passive smokingduring pregnancyand no other smoking exposurewere more likely to develop wheezeup to the age of 2 years (OR 1.11, 95% CI 1.03-1.20) compared with unexposed children. Risk of wheezewas further increased by children's postnatal passive smoke exposurein addition to their mothers' passive exposureduring pregnancy (OR 1.29, 95% CI 1.19-1.40) and highest in children with both sources of passive exposureand mothers who smokedactively during pregnancy (OR 1.73, 95% CI 1.59-1.88). Risk of wheezeassociated with tobacco smoke exposurewas higher in children with an allergic versus nonallergic family history. Maternal passive smoking exposureduring pregnancy is an independent risk factor for wheezein children up to the age of 2 years. Pregnant females should avoid active and passive exposureto tobacco smokefor the benefit of their children's health.