The joint effect of maternal smoking during pregnancy and maternal pre-pregnancy overweight on infants' term birth weight

Background: It is well known that maternal smoking during pregnancy and maternal pre-pregnancy overweight have opposite effects on the infants' birth weight. We report on the association of the combination between both risk factors and the infants' birth weight. Methods: We studied 3241 infants born at term in the PIAMA birth cohort. Maternal smoking during pregnancy and pre-pregnancy height and weight were self-reported. Multivariable regression analysis was performed to assess the associations between infants of mothers who only smoked during pregnancy, who only had pre-pregnancy overweight and who had both risk factors simultaneously, on term birth weight and the risk of being SGA or LGA. Results: Of 3241 infants, 421 infants (13%) were born to smoking, non-overweight mothers, 514 (15.8%) to non-smoking, overweight mothers, 129 (4%) to smoking and overweight mothers an