Cohort profile: Mothers who use substances and their children in British Columbia, Canada

Introduction: Perinatal substance use is a growing public health challenge in the province of BC. A population-based cohort was established using linked health administrative data to underpin three research studies that will evaluate: 1) the effectiveness of specialized acute care for pregnant people who use substances; 2) the comparative effectiveness of different medication regimens for the treatment of perinatal opioid use disorder (OUD); and 3) the longitudinal association between maternal substance use and child health outcomes. Methods: The population-based cohort includes all individuals in British Columbia (BC), Canada, who delivered an infant from April 1, 2000–March 31, 2022, and who had an indication of substance use in their health administrative records between one year prior to the first pregnancy-related healthcare contact and time of delivery. Individual-level data for mothers and children were linked across ten population-level databases, which include information on demographics, healthcare utilization, drug dispensations, incarceration in provincial prisons, maternal and newborn health outcomes, receipt of housing and income assistance, and deaths and underlying causes. Results: We identified 38,670 mothers with substance use disorders and their children (n = 45,823), with a median of 9 (interquartile range: 5–15) years of follow-up available. At the time of delivery, mothers ranged from