How heavy is the price of smoking? Estimating the effects of prenatal smoking on child weight outcomes

Existing evidence suggests that maternal smoking during pregnancy leads to a decline in birthweight and a higher risk of obesity during early childhood years. However, the causal nature of the latter relationship is not credibly established. This study advances the literature by estimating the causal impact of motherʻs smoking during pregnancy on child bodyweight outcomes, from birth through age five. We use a nationally representative sample of children and mothers from the United States National Longitudinal Surveys. We model childrenʻs body weight as a function of motherʻs smoking during pregnancy. Our identification technique utilizes the instrumental variable strategy to exploit plausibly exogenous variation in smoking behaviour of mothers prompted by changes in federal and state-level tobacco tax rates at the time of conception. Consistent with prior literature, our instrumental variable estimates suggest children of smokers weigh significantly less at birth than children of nonsmokers (an estimated decline of 0.53 kg). However, there is no credible evidence that these children are more likely to be overweight during early childhood.