Weight gain during the first year of life in relation to maternal smoking and breast feeding in Norway

Objective-To assess the weight gain during the first year of life in relation to maternal smoking during pregnancy and the duration of breastfeeding. Design-This was a one year cohort study. Setting-The city of Oslo, Norway. Participants-Altogether 3020 children born in Oslo in 1992-93. Children were divided into three groups as follows: 2208 born to non-smoking mothers, 451 to mothers who were tight smokers (<10 cigarettes per day), and 261 to mothers who were heavy smokers (greater than or equal to 10 cigarettes per day). Main results-The mean birth weights were 3616 g, 3526 g, and 3382 g and 1 year body weights were 10 056 g (gain 6440 g per year), 10141g (6615 g), and 10158 g (6776 g) in children of non-smoking and light and heavy smoking mothers respectively. Cox regression analysis showed that children of heavy smokers were 2.0 (95% confidence interval, 1.7, 2.3) times and children of light smokers 1.3 (1.2, 1.5) times more Likely to have stopped breast feeding during their first year of life compared with children whose mothers were non-smokers. Linear regression analysis, adjusting for confounders, showed that weight gain was slower in breast fed children than in those who were not breast fed (-38 g (-50, -27) per month of breast feeding). Compared with children of nonsmokers, the adjusted weight gain was 147 g (40, 255) per year greater in children of light smokers and 184g (44, 324) per year in children of heavy smokers. Conclusion-Children catch up any losses in birth weight due to maternal smoking, but some of the catch up effect is caused by a shorter duration of breast feeding in children of smoking mothers.