Maternal smoking very early in pregnancy is related to child overweight at age 5-7 y.

Background: Despite being associated with lower birth weight, maternal smoking in the last 2 trimesters of pregnancy has been associated with increased risk of offspring overweight in several studies. To date, only one study has examined whether smoking in the first trimester only, which is not associated with birth weight, is also associated with childhood overweight.

Objective: This study uses prospective data to examine associations between maternal smoking in the first compared with later trimesters of pregnancy and child overweight at age 5-7 y.

Design: Data from a prospective cohort of 369 Spanish children born in 1997-1998 were used. Logistic regression was used to estimate associations between maternal smoking during different time periods and odds of child overweight later in life.

Results: Maternal smoking during the first trimester was more strongly associated with overweight (adjusted odds ratio: 2.65; 95% CI: 1.26, 5.54) than smoking later in pregnancy (1.88, 0.85, 4.15). Smoking limited to the first month of pregnancy was also associated with child overweight. Neither paternal smoking nor maternal smoking before or after pregnancy was associated with child overweight. Significant interactions with breastfeeding duration indicated that first-trimester smoking was associated with overweight only among children breastfed for <6 mo, suggesting prolonged breastfeeding may help to counter adverse effects of smoking in early pregnancy.

Conclusions: These data suggest maternal smoking very early in pregnancy may increase risk of later overweight in children and provide further support for promoting smoking cessation before rather than during early pregnancy. Further studies are needed to confirm these results.