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: 1.1-1.7, P = 0.006 and 1.8, 95% CI: 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.