Maternal smoking during pregnancy and offspring overweight: is there a dose-response relationship? An individual patient data meta-analysis.

BACKGROUND/OBJECTIVES: A number of meta-analyses suggest an association between any maternal smoking in pregnancy and offspring overweight obesity. Whether there is a dose-response relationship across number of cigarettes and whether this differs by sex remains unclear. SUBJECT/METHODS: Studies reporting number of cigarettes smoked during pregnancy and offspring BMI published up to May 2015 were searched. An individual patient data meta-analysis of association between the number of cigarettes smoked during pregnancy and offspring overweight (defined according to the International Obesity Task Force reference) was computed using a generalized additive mixed model with non-linear effects and adjustment for confounders (maternal weight status, breastfeeding, and maternal education) and stratification for sex. RESULTS: Of 26 identified studies, 16 authors provided data on a total of 238,340 mother-child-pairs. A linear positive association was observed between the number of cigarettes smoked and offspring overweight for up to 15 cigarettes per day with an OR increase per cigarette of 1.03, 95% CI = [1.02-1.03]. The OR flattened with higher cigarette use. Associations were similar in males and females. Sensitivity analyses supported these results. CONCLUSIONS: A linear dose-response relationship of maternal smoking was observed in the range of 1-15 cigarettes per day equally in boys and girls with no further risk increase for doses above 15 cigarettes.