Examination of the relationship between birthweight, cigarette smoking during pregnancy and maternal weight gain.

Abstract

SummaryThere has been no reported systematic exploration of the hypothesis that the low birthweight of infants whose mothers smoke in pregnancy is mediated by depressed caloric intake. Using gestational weight gain as an index of energy balance, we have studied this question among 162 mothers and their liveborn singleton infants, in a poor, black, urban American community. Smoking mothers had lower mean weekly weight gain (0.73 versus 0.90 pounds per week; t=2.63; p<0.01), and a strong and highly significant gradient of decreasing weight gain with increased amount smoked (0.017 fewer pounds per week gained per additional cigarette per day; F=12.45; p<0.005). Women who stopped smoking before delivery had higher weight gain than those who continued; the difference was not significant, but numbers were small. Regression analyses were performed in order to quantitate the unique and joint contributions of smoking and change in maternal weight to birthweight. At least half, and usually closer to three‐quarters, of the effect of smoking on birthweight was jointly shared with maternal weight change. Smoking is in all likelihood depressing fetal growth, in large part, by depression of caloric intake, reflected by lower maternal weight gain. No other examined differences between smokers and non‐smokers accounted for these differences.