Trends in Opioid Agonist Treatment for Opioid Dependence During Pregnancy: A Population‐Based Study in New South Wales 2005–2021

ABSTRACT Introduction The objective of this study was to examine trends in opioid agonist treatment (OAT) during pregnancy for opioid dependence, by OAT type (methadone, buprenorphine) and during‐pregnancy OAT type change. Methods Data linkage study. The cohort included pregnancies resulting in childbirth among people who received OAT within 4 years prior to birth, New South Wales, 1 January 2005–31 December 2021. We calculated the prevalence of OAT during pregnancy by OAT type and year of birth; prevalence rate ratios (PRR) and proportions experiencing OAT type change during pregnancy. Results The cohort included 5212 childbirths among 3303 people. OAT was received in 4102 (78.7%) pregnancies. The annual prevalence of OAT during pregnancy was 77.2% in 2005, 86.2% in 2012 and 63.2% in 2021 (PRR 0.99; 95% confidence interval [CI] 0.99–1.00). Between 2005 and 2021, methadone use during pregnancy decreased from 70.9% to 37.4% (PRR 0.97; 95% CI 0.96–0.98) while buprenorphine use increased from 12.3% to 29.3% (PRR 1.07; 95% CI 1.06–1.08). Overall, changes in OAT type occurred in 226 pregnancies (5.5%). Among 971 pregnancies initially on buprenorphine, methadone was later used among 193, with this proportion decreasing over time. Of the 3131 pregnancies initially on methadone, buprenorphine was later used among only 33. Discussion and Conclusions Three in four people in the cohort received OAT during pregnancy, with no statistically significant change in annual prevalence over the 2005–2021 period. Given prior evidence indicating higher rates of treatment discontinuation with buprenorphine versus methadone, the increased buprenorphine use during pregnancy highlights the need for targeted strategies to support treatment retention.