The Association between Maternal Smoking during Pregnancy and Childhood Obesity Persists to the Age of 9-10 Years

Background: We previously reported that a number of factors related to maternal lifestyle during early pregnancy, including smoking, are associated with childhood obesity at 5 years of age. In the present study, we investigated whether the association with maternal smoking persisted to the age of 9-10 years. Methods: The study population comprised children born between April 1, 1991 and March 31, 1999, and their mothers. The dependent variables-childhood overweight and obesity at 5 and 9-10 years of age-were defined according to internationally acknowledged cut-off values. Maternal smoking during early pregnancy was used as the independent variable. Results: Mothers who completed a specifically designed questionnaire gave birth to a total of 1644 infants during the study period. Anthropometric data were collected from 1302 of these children during medical checkups at 9-10 years of age (follow-up rate: 79.2%). Maternal smoking during early pregnancy was associated with obesity in 9- to 10-year-old children (adjusted odds ratio, 1.91; 95% confidence interval, 1.03-3.53). However, the point estimates at the age of 9-10 years were considerably lower than those at the age of 5 years. Conclusions: Our results suggest that fetal environment, including exposure to maternal smoking, continues to be associated with childhood obesity at the age of 9-10 years.