Maternal smoking during lactation: relation to infant size at one year of age.

This study was conducted to test the hypothesis that breast-fed infants of smokers are smaller in size at 1 year of age than breast-fed infants of nonsmokers. Three groups of infants were selected from all singletons born to women who were seen for prenatal care in their 6th month of pregnancy at a health maintenance organization in Seattle, Washington, between January 1982 and April 1983. Breast-fed infants of smokers (n = 74) were compared with breast-fed infants of nonsmokers (n = 195) and with bottle-fed infants of smokers (n = 64). Mothers were interviewed at 1 and 3 months after delivery; both the mother and the infant were seen at 1 year. Among breast feeders, smokers' infants were twice as likely as nonsmokers' infants to have body mass more than 1 standard deviation above the mean (relative risk = 2.04, 95% confidence interval 1.15-3.61). This relation persisted after control for gestational age and weight at birth, length of lactation, mother's size and diet, exposure to other drugs in breast milk, and all other variables measured in this study. Every 10 cigarettes smoked while breast feeding predicted an additional 3% infant body mass at 1 year. In summary, breast-fed infants of smokers in this study gained more weight after birth than the other two groups; at 1 year of age, they were heavier and had significantly higher body mass. Reasons for this paradoxical finding are explored.

Maternal alcohol use during breast-feeding and infant mental and motor development at one year.

The detrimental effects of maternal drinking during pregnancy on fetal health have been documented. The consequences for infants of maternal drinking during breast-feeding are unknown, but research in animals suggests that the infant could be affected by exposure to alcohol through the mother's milk. In a study of 400 infants born to members of a health maintenance organization, we investigated the relation of the mother's use of alcohol during breast-feeding to the infant's development at one year of age. Mental development, as measured by the Bayley Mental Development Index (MDI), was unrelated to maternal drinking during breast-feeding. However, motor development, as measured by the Psychomotor Development Index (PDI), was significantly lower in infants exposed regularly to alcohol in breast milk (after alcohol exposure during gestation was controlled for), with a dose-response relation (P for linear trend, 0.006). The infants of breast-feeding mothers who had at least one drink daily had a mean PDI score of 98, whereas the infants exposed to less alcohol in breast milk had a mean PDI score of 103 (95 percent confidence interval for the difference of the two means, 1.2 to 9.8). The effect was more pronounced when mothers who supplemented breast-feeding with formula were excluded from the analysis. The association persisted even after we controlled for more than 100 potentially confounding variables, including smoking and other drug use during pregnancy and in the postpartum period. We conclude that ethanol ingested through breast milk has a slight but significant detrimental effect on motor development, but not mental development, in breast-fed infants.