Background
Maternal smoking is associated with a number of adverse outcomes with a dose‐dependent increase in risk. The aim of this study was to evaluate the obstetric and perinatal outcomes in women who smoked during pregnancy.

Methods
This was a retrospective cohort study of women who smoked during pregnancy and birthed at a major perinatal centre in Australia between January 2000 and April 2017. The study cohort was compared to a cohort of women who did not smoke in pregnancy. Smoking status was ascertained on history and included all types of smoking. Demographic characteristics and obstetric, intrapartum and perinatal outcomes were compared between the two groups.

Results
The study cohort included 20 477 (14.6%) women who smoked during pregnancy and 119 396 controls. Women who smoked tended to be younger, of higher body mass index (BMI), Caucasian and Indigenous ethnicity. Smokers were less likely to be nulliparous, but more likely to be hypertensive and have a lower socioeconomic status compared to non‐smokers. Women who smoked were more likely to have a caesarean section for non‐reassuring fetal status (adjusted odds ratio (aOR) 1.16, 95%CI 1.07–1.26, P < 0.001). The infants of women who smoked were more likely to be born preterm, have a lower median birth weight and birth weights <10th (aOR 1.76, 95%CI 1.66–1.86, P < 0.001) and <5th centile (aOR 2.00, 95%CI 1.86–2.16, P < 0.001). Neonatal outcomes in the smoking cohort were worse with an increase in neonatal intensive care unit admission (aOR 1.34, 95%CI 1.27–1.43, P < 0.001), severe acidosis (aOR 1.41, 95%CI 1.27–1.43, P < 0.001) and a composite of severe neonatal outcomes (18.0% vs 12.0%, aOR 1.35, 95%CI 1.28–1.43, P < 0.001). Conclusion Women who smoke in pregnancy have worse obstetric and perinatal outcomes compared to controls and should be managed as high risk.