Early intrauterine exposure to tobacco-inhaled products and obesity.

An association between maternal smoking during pregnancy and offspring obesity has been reported. This study assessed the impact of maternal smoking during the first trimester. Data on 4,974 German children aged 5-6 years were obtained at school entry health examinations in 2001-2002 in Bavaria. Obesity was defined by body mass index using International Obesity Task Force cutpoints. Prevalence of obesity was 1.9% (95% confidence interval (CI): 1.5, 2.4) in offspring of never smokers, 4.5% (95% CI: 2.9, 6.7) for maternal smoking during the first trimester only, and 5.9% (95% CI: 3.8, 8.7) for maternal smoking throughout pregnancy. Unadjusted odds ratios were higher for maternal smoking throughout pregnancy (odds ratio = 3.23, 95% CI: 2.00, 5.21) compared with the first trimester only (odds ratio = 2.41, 95% CI: 1.49, 3.91). Adjusted odds ratios were similar: 1.70 (95% CI: 1.02, 2.87) for maternal smoking throughout pregnancy and 2.22 (95% CI: 1.33, 3.69) for maternal smoking in the first trimester only. When modeled together, no statistically significant difference in obesity risk was found between maternal smoking in the first trimester compared with throughout pregnancy. The effect of intrauterine tobacco exposure on childhood obesity may depend largely on cigarette smoking during the first trimester, whereas the additional impact of smoking throughout pregnancy might be due to confounding by sociodemographics. Women should be encouraged to quit smoking prior to conception.