Objective: The purpose of this study was to examine the relationship among methadone maintenance treatment, perinatal outcomes, and neonatal abstinence syndrome.

Study design: This was a retrospective cohort study of 61,030 singleton births at a large maternity hospital from 2000-2007.

Results: There were 618 (1%) women on methadone at delivery. Methadone-exposed women were more likely to be younger, to book late for antenatal care, and to be smokers. Methadone exposure was associated with an increased risk of very preterm birth <32 weeks of gestation (adjusted odds ratio [aOR], 2.47; 95% confidence interval [CI], 1.40-4.34), being small for gestational age <10th percentile (aOR, 3.27; 95% CI, 2.49-4.28), admission to the neonatal unit (aOR, 9.14; 95% CI, 7.21-11.57), and diagnosis of a major congenital anomaly (aOR, 1.94; 95% CI, 1.10-3.43). There was a dose-response relationship between methadone and neonatal abstinence syndrome.

Conclusion: Methadone exposure is associated with an increased risk of adverse perinatal outcomes, even when known adverse sociodemographic factors have been accounted for. Methadone dose at delivery is 1 of the determinants of neonatal abstinence syndrome.