This review summarizes the epidemiology and consequences of maternal smoking in pregnancy, with emphasis on the adverse effects on birth outcomes. In developed countries, approximately 15%, and in developing countries, approximately 8% of women
smoke cigarettes, and adolescents and women from lower socioeconomic groups are more likely than other women to
smoke while pregnant. Maternal smoking during pregnancy is the largest modifiable risk factor for
intrauterine growth restriction. A meta-analysis of recent studies showed that the pooled estimate for reduction of mean
birthweight was 174 g (95% confidence limits 132-220 g). Other studies confirm a weaker association between maternal smoking and
preterm birth. The population attributable risk of low
birthweight due to maternal smoking in the UK is estimated to be 29-39%. Tobacco
smoke toxins damage the placenta and may lead to
placental abruption, abortion or
placenta praevia. Infants of mothers who
smoke in pregnancy are at an increased risk of respiratory complications including
asthma,
obesity and, possibly, behavioral disorders. These effects may be dose-related, as there is good evidence that mean
birthweight decrements are greater with increased numbers of cigarettes smoked during pregnancy.
Cotinine is a useful
indicator of tobacco
smoke exposure in pregnant women and higher levels in body fluids have been related to lower
birthweights. Maternal genetic polymorphisms of the
cytochrome P (CYP)450 and
glutathione-S-transferase (GST) subfamilies of metabolic genes influence the magnitude of the effect of
nicotine exposure on birth outcomes through their influence on
nicotine metabolism. Greatly increased risk of cigarette
smoke-induced diseases, including low
birthweight, has been found in individuals with susceptible genotypes. Interventions to control maternal smoking are also considered.