Cessation of smoking during pregnancy improves foetal growth and reduces infant morbidity in the neonatal period. A population-based prospective study.

All pregnant women in Uppsala county in 1987 were questioned on three different occasions about smoking habits, socio-demographic factors and obstetric history. After delivery, information was collected regarding their children. Twenty percent of the mothers continued to smoke during pregnancy, while 8% stopped smoking. The mean birth weight of infants of smokers was 3378 g and of non-smokers 3589 g. The difference was significant (p < 0.001) and persisted after statistical adjustment for maternal age, parity and educational level. Perinatal morbidity (admission to the Department of Neonatology) was higher in the smoking group (11.4% versus 8.8%, p < 0.05). The proportion of infants with a birth weight less than 2500 g and that of small-for-gestational-age infants were 60% and 100% greater, respectively, in the smoking group. The mean birth weight and perinatal morbidity rate in infants of mothers who stopped smoking were almost identical to those in infants of non-smokers. Cessation of smoking improves foetal growth and perinatal health.