Maternal smoking during lactation: relation to growth during the first year of life in a Dutch birth cohort

A recent article by Little et al. (Am J Epidemiol 1994;140:544-54) reported that infants in Seattle, Washington, who were breastfed by mothers who smoked gained more weight than either infants who were breastfed by mothers who did not smoke or infants who were bottle-fed by mothers who smoked. In this study, the authors aimed to verify this result with the use of data from the Social Medical Survey of Children Attending Child Health Clinics (SMOCC) cohort, a nationally representative cohort of 2,151 children born in the Netherlands in 1988-1989. During the first year of life, data on type of milk feeding, weight, length, and head circumference were collected at 1, 2, 3, 6, 9, and 12 months of age. Infants of smokers who were mainly breastfed in the first 3 months of life (n = 117) were compared with similarly breastfed infants of nonsmokers (n = 572), with infants of smokers who had been mainly bottle-fed (n = 270), and with infants of nonsmokers who had been mainly bottle-fed (n = 535). The authors failed to observe any additional increase in body mass, length, or head circumference in infants of breastfeeding smokers compared with infants of the three other groups. When the authors used all of their data to study growth with a multivariate longitudinal regression model (general estimating equations (GEE) model), the data showed clearly reduced growth in breastfed children (limited to the period after the second month of life) and some "catch-up" growth in body mass and head circumference in children with intrauterine exposure to tobacco.