Maternal smoking in relation to the incidence of early neonatal jaundice.

A case-control study was carried out to investigate the association between maternal smoking during pregnancy and the risk of early neonatal jaundice. A total of 1,569 cases of neonatal jaundice (2.7% of all singleton births) were identified from the 1984 Washington State birth certificates as having a bilirubin level greater than 10 mg/dl within the first 2 days of life. 2,336 nonjaundiced infants were randomly selected to serve as controls. Information regarding smoking during pregnancy was also obtained from the birth certificates. After excluding infants with known risk factors for neonatal jaundice, 912 cases and 1,752 controls were available for analyses. Infants whose mother smoked cigarettes during pregnancy were at lower risk of neonatal jaundice (odds ratio = 0.81; 95% confidence interval = 0.66-0.99) relative to infants of nonsmokers. This relative risk changed very little after adjusting separately for maternal age, infant's gender, number of prior pregnancies, number of prenatal visits, marital status and number of prior fetal deaths. There was suggestive evidence that this apparent protective effect may be operating only among normal and high-birth-weight infants.