Maternal cigarette smoking during pregnancy and infant ponderal index at birth in the Swedish Medical Birth Register, 1991-1992

Objectives. This study examined the effect of maternal smoking during pregnancy on infant body proportion. Methods. The ponderal index, defined as birthweight divided by crown-heel length cubed, was examined in 207 607 infants from the Swedish Medical Birth Register for 1991 and 1992. Results. Infant ponderal index was used as the outcome variable in an ordinary least squares continuous regression, which included early pregnancy smoking status, gestational age, and birthweight among the predictors. Ponderal index increased by 0.030 (± 0.0014) among infants of moderate smokers and by 0.040 (± 0.0017) among infants of heavy smokers, showing a dose response. Conclusions. Smoking differentially alters the trajectory of weight vs length growth in the fetus.