The interaction between maternal smoking, illicit drug use and alcohol consumption associated with neonatal outcomes

Background The adverse effects of smoking on neonatal outcomes, such as small-for-gestational-age (SGA), has been extensively studied however, the consequences of smoking combined with alcohol and/or drug use is less clear. Methods This retrospective observational study analyzed clinical and sociodemographic details of 40156 women who delivered a singleton baby between the years 2011 and 2015. Results Compared with women who had never smoked, smokers who did not engage in alcohol or drug use had an odds ratio (OR) of delivering a baby who was SGA of 3.2 (95% CI: 3.1-3.5). Smokers who used illicit drugs in isolation or in combination with alcohol during pregnancy had higher ORs for SGA (1.4, 95% CI: 1.1-11, P = 0.006 and 1.8, 95% 0: 1.2-2.7, P = 0.007) compared to women who smoked but did not engage in alcohol or drug use in pregnancy. These women also delivered babies with lower mean birthweights (125 g, P < 0.001 and 181.4 g, P = 0.003) and head circumferences (0.4 cm, P < 0.001 and 0.3 cm, P = 0.048). Women who smoked and used alcohol, but not illicit drugs were not associated adverse outcomes above that of smoking in isolation. Conclusion Illicit drug use combined with maternal smoking during pregnancy increases the risk of adverse neonatal outcomes above that of smoking in isolation.