David Rush

EXAMINATION OF THE RELATIONSHIP BETWEEN BIRTHWEIGHT, CIGARETTE SMOKING DURING PREGNANCY AND MATERNAL WEIGHT GAIN

There 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.

A partial explanation of superior birth weights among foreign‐born women

This study of 766 black women reexamined the issue of advantage in birthweight and length of gestation in foreign-born women and confirms the reported higher birthweights among that group. Subjects were new registrants for prenatal care at a public clinic in Harlem, New York City, 1971-73, and were part of a randomized trial of nutritional supplementation during pregnancy. 3 nativity groups were represented: New York City, southern United States, and foreign countries. Despite the standard selection of all subjects for high risk for low birthweight, foreign-born women had only 3.8% of births under 2500 grams in contrast to 15.6% among the southern women, and 18% among New York City natives. 6 sets of variables were examined in relation to birthweight outcome. An average birthweight advantage of 218 grams for the foreign-born was found to be associated with higher childhood social status and more positive health behaviors.

Effects of smoking on pregnancy and newborn infants.

Davies and associates along with this researcher observed depressed weight gain among mothers who smoked cigarettes during pregnancy; this depressed gain was dose-related and in both studies statistically accounted for most of the effects of smoking on birth weight. Meyer asserts that she has not observed depressed weight gain with smoking, but she fails to present the distribution of maternal weight gain by smoking separately for light and moderate smokers. Since the effect on light smokers observed in the other studies is weak, a strong effect on the smaller number of heavy smokers might obscure Meyers data. On reviewing the English language literature, Kass and this researcher found an intense interaction of social status with smoking related to the potential lethality in the fetus. Upper-status smokers protect their fetuses from the effects of smoking whereas lower-status smokers do not. There is now evidence that this partial protection is likely mediated by a sustained weight gain in pregnancy. Meyers assertion that the depressed weight gain of the smoking mothers in the studies of Davies and this researcher reflected lowered fetal weight is impossible. Birth weights were depressed by a few hundred grams; maternal weight gains among heaviest smokers were depressed by more than 10 times that amount.