Effect of continuing or stopping smoking during pregnancy on infant birth weight, crown-heel length, head circumference, ponderal index, and brain:body weight ratio.

The objective of this study was to determine whether stopping smoking between the first prenatal care visit and the 32nd week of pregnancy affects the smoking-associated changes in five infant anthropometric indices. The study population consisted of 15,185 births in the Swedish Medical Birth Register from 1991 and 1992. The associations between birth weight, crown-heel length, head circumference, ponderal index, brain:body weight ratio, maternal smoking status at the first prenatal care visit and at 32 weeks' gestation, and other maternal and infant characteristics were assessed using multivariate linear regression. The infants of 946 women who stopped smoking before week 32 of pregnancy were statistically indistinguishable from the 9,802 infants of nondaily smokers in terms of birth weight, head circumference, and brain:body weight ratio, but they retained a significant deficit in crown-heel length of 0.23 cm (standard error, 0.08) and a significant elevation in ponderal index of 0.027 (standard error, 0.009). In this study, stopping smoking between the first prenatal care visit and week 32 of pregnancy prevented smoking-associated deficits in infant birth weight, head circumference, and brain:body weight ratio, but did not completely prevent deficits in crown-heel length in comparison with nonsmokers' infants of the same age, and did not prevent elevation of ponderal index in comparison with nonsmokers' infants of the same weight and age.