INTRODUCTION: As perinatal drug overdoses continue to rise, reliable approaches are needed to monitor overdose trends during pregnancy and postpartum. This analysis aimed to determine the sensitivity, specificity, positive predictive value, and negative predictive value of ICD-9/10-CM codes for drug overdose events among people in the MATernaL and Infant clinical NetworK (MAT-LINK) with medication for opioid use disorder during pregnancy. METHODS: People included in this analysis had electronic health record documentation of medication for opioid use disorder and a known pregnancy outcome from January 1, 2014, through August 31, 2021. Data were analyzed during pregnancy through 1 year postpartum. The Centers for Disease Control and Prevention's drug overdose case definitions were used to categorize overdose based on ICD-9/10-CM codes. These codes were compared to abstracted electronic health record data of any drug overdose. Analyses were conducted between May 2023 and May 2024. RESULTS: Among 3,911 pregnancies with electronic health record-documented medication for opioid use disorder, the sensitivity of ICD-9/10-CM codes for capturing drug overdose during pregnancy was 32.7%, while specificity was 98.5%, positive predictive value was 23.4%, and negative predictive value was 99.0%. The sensitivity of ICD-9/10-CM codes for capturing drug overdose postpartum was 30.9%, while specificity was 98.4%, positive predictive value was 25.9%, and negative predictive value was 98.8%. CONCLUSIONS: The sensitivity and positive predictive value of ICD-9/10-CM codes for capturing drug overdose compared with abstracted electronic health record data during the perinatal period was low in this cohort of people with medication for opioid use disorder during pregnancy, though the specificity and negative predictive value were high. Incorporating other data from electronic health records and outside the healthcare system might provide more comprehensive insights on nonfatal drug overdose in this population.