Aim and Methods A cross sectional survey was conducted to investigate the dose response association of maternal smoking during pregnancy and subsequent risk of childhood overweight or obesity. 1964 schoolchildren aged 5–11 years in Merseyside were recruited and parents completed a standardised questionnaire. Data on dose and duration of pregnancy smoking exposure was requested. Body Mass Index (BMI) Z scores of children were calculated.

Results Of 684 (34.8%) mothers who smoked during pregnancy, 42.5% were heavy smokers (>10 cigarettes daily). Overall 14% of children were overweight and 9.1% obese. The corresponding proportions in children of mothers who smoked were 26.2% and 11.5% respectively, compared to the non-smokers (p = 0.07 and p = 0.01 respectively). There was an increase in the mean BMI in children with increasing numbers of daily cigarettes smoked by mothers and an increased prevalence of childhood obesity and overweight in heavy smokers compared to light smokers (p = 0.01 and p = 0.04) or none smokers (p<0.001 and p = 0.003 respectively). Regression analysis adjusting for household socio-economic status, and child age showed that maternal smoking during pregnancy had an independent association for developing obesity in later childhood (adjusted OR: 1.8, 95% CI 1.3 to 3.4, p = 0.001).

Conclusion A dose-response association was observed between maternal pregnancy smoking and the risk of developing overweight or obesity in childhood.