Buprenorphine Exposure in Pregnancy Is Linked to Reduced Fetal Femur Length and Abdominal Circumference [ID 3448]

INTRODUCTION: Maternal opioid use is associated with small-for-gestational-age infants. Emerging data from our institution suggest a potential increased incidence of shortened femur length in fetuses with buprenorphine exposure. This study aimed to evaluate whether buprenorphine use is associated with altered femur length and other fetal growth parameters and to explore a possible dose–response relationship. METHODS: Fetal anatomy scans were performed at ∼20 weeks of gestation, with serial growth scans starting at 32 weeks for patients on medication-assisted therapy (MAT) due to risk of growth restriction. We retrospectively reviewed ultrasound reports for three groups: low-dose MAT (less than 2 mg buprenorphine daily; n=127), high-dose MAT (greater than 8 mg daily; n=103), and controls without known buprenorphine exposure (n=212). RESULTS: At the anatomy scan, femur length was decreased in both high-dose ( P =.02) and low-dose ( P =.0004) buprenorphine groups versus controls. This persisted into the third trimester ( P =.00005 and P =.004, respectively), when estimated fetal weight was also reduced ( P =.006 and P =.02, respectively). High-dose exposure was further associated with decreased abdominal circumference ( P =.03), biparietal diameter ( P =.001), and mean cephalic index ( P =.02) in the third trimester. Birth weight was lower in the high-dose group compared with controls ( P =.0003). CONCLUSIONS/IMPLICATIONS: Fetal buprenorphine exposure is associated with decreased femur length at the anatomy scan and in the third trimester. High-dose exposure exhibits a broader effect on growth parameters, suggesting a dose–response relationship. These findings should not limit access to buprenorphine for pregnant persons, given the risks of withdrawal and relapse, but remain vital for well-informed counseling and antenatal surveillance.