Impact of timing of methadone initiation on perinatal outcomes following delivery among pregnant women on methadone maintenance therapy in Ontario

Background and Aims — Methadone maintenance therapy (MMT) is associated with improved outcomes for children exposed to maternal opioid dependence in utero. We examined Ontario's population of pregnant women on MMT and determined the impact of timing of MMT initiation on perinatal outcomes.

Design — Cohort study.

Setting — Ontario, Canada.

Participants — Women eligible for public drug benefits and on MMT during pregnancy between 2005 and 2015.

Measurements — We stratified women based on their timing of MMT initiation: (1) stabilized prior to conception, (2) newly initiated prior to conception, (3) initiation in trimester 1, (4) initiation in trimester 2 or (5) initiation in trimester 3. The primary outcomes in the multivariable logistic regression analysis were key perinatal health indicators: small for gestational age, preterm birth, congenital anomalies, severe maternal morbidity, caesarean section and induced labor. Secondary outcomes were specific to maternal opioid dependence: neonatal abstinence syndrome (NAS), admission to a neonatal intensive care unit (NICU), NAS treatment, removal from mother's custody at hospital discharge and neonatal death.

Findings — Among 1842 women on MMT during pregnancy, 87.6% (n = 1614) initiated MMT before conception. Almost a quarter of their infants (22.2%; n = 408) were born small for gestational age, 17.5% (n = 323) were preterm and 5.9% (n = 109) were born with a congenital anomaly. The odds of primary outcomes occurring did not differ based on timing of methadone initiation; however, infants of mothers who initiated methadone during pregnancy had up to a fourfold increase in the odds of social services removal at the hospital [adjusted odds ratio (aOR) range = 3.70-4.19] compared with those whose mothers were stabilized on MMT prior to conception.

Conclusions — Later initiation of methadone maintenance therapy among pregnant women in Ontario, Canada has not clearly been found to be related to most key perinatal adverse health outcomes.