BACKGROUND: Although urine drug testing can have vast legal and social ramifications, its interpretation during pregnancy and after birth remains not well understood. Fentanyl metabolism is altered by an individual's genetics, history of opioid use, and liver function. However, little is known about the clearance of fentanyl or its primary metabolite, norfentanyl, in the peripartum period. OBJECTIVE: We sought to identify and describe cases of delayed urine norfentanyl clearance in the pregnancy and postpartum period within our institution. STUDY DESIGN: This study described 3 cases of delayed urine norfentanyl clearance in pregnant and postpartum individuals in a colocated obstetrics, postpartum, and addiction medicine program. This program included prescriptions for medication for opioid use disorder and weekly urine drug testing with fentanyl immunoassay with reflex confirmation testing with liquid chromatography-tandem mass spectrometry for positive results with a limit of detection of 2.5 ng/mL. RESULTS: Low levels of norfentanyl (