PURPOSE: Opioid agonist treatment (OAT) is the first-line treatment for opioid dependence during pregnancy and recommended for at least one year postpartum or until a strong maternal-infant bond and stable family environment is established. Evidence on postpartum OAT retention is limited. We examined retention rates and associated maternal characteristics.

METHODS: We linked OAT prescription authority to perinatal, mortality, and other data sources. We identified all opioid-dependent women who gave birth in New South Wales, Australia (1 January 2004-31 March 2020) while receiving OAT. We defined retention at 90, 180, and 365 days postpartum as continuous treatment over each period. We calculated retention rates and used generalised linear modelling to examine association between retention and maternal socio-demographic and clinical factors.

RESULTS: There were 3933 childbirths among 2514 women on OAT. Retention rates were 93.3% (n = 3670) at 90 days, 88.4% (n = 3475) at 180 days, and 78.5% (n = 3086) at 365 days. Retention at 180 days was lower for those who gave birth after 2015, were Indigenous, had recent conviction or incarceration, initiated OAT after conception, received buprenorphine, or had a mental illness. We observed similar association patterns at 90 and 365 days.

CONCLUSIONS: Among women on OAT at childbirth, postpartum treatment retention was high but varied across subgroups. Lower retention among women who initiated OAT late in pregnancy or with social or clinical risk factors highlights the need for targeted support. Lower buprenorphine retention warrants ongoing monitoring and tailored care, particularly in settings where it is the preferred treatment during pregnancy.