We studied the associations of maternal pre-pregnancy body mass index and gestational weight gain with risks of preschool wheezing in offspring and explored the role of growth, infectious and atopic mechanisms.This substudy of 4656 children was embedded in a population-based birth cohort. Information about maternal pre-pregnancy weight, gestational weight gain and wheezing at the ages of 1-4 years was obtained by either physical measurements or questionnaires.Among mothers with a history of asthma or atopy, maternal pre-pregnancy obesity was associated with an overall increased risk of preschool wheezing (odds ratio 1.47, 95% confidence interval 1.12-1.95). Also, each standard deviation increase of gestational weight gain was associated with an increased overall risk of preschool wheezing (1.09, 1.04-1.14), was independent of pre-pregnancy body mass index and was not different between mothers with and without a history of asthma or atopy. Child's growth, respiratory tract infections or eczema did not alter the results.Mothers with pre-pregnancy obesity and a history of asthma or atopy, and mothers with higher gestational weight gain showed higher risks of wheezing in their offspring. These associations could not be explained by growth, infectious or atopic mechanisms. Further research is needed to identify underlying mechanisms and long-term consequences. @ERSpublications Pre-pregnancy obesity associated with increased risk of wheezing in offspring, if mothers have history of asthma or atopy

Cape Verdean, Dutch Antillean, Surinamese-Creole, and Surinamese-Hindustani children had increased risks of eczema in the first 4 years of life. Environmental and genetic risk factors partly weakened these associations.