Association between Maternal Buprenorphine Use and Fetal Head Circumference

The objective of this study was to evaluate the effect of intrauterine buprenorphine exposure during pregnancy on fetal head circumference.

This retrospective cohort study reviewed fetal ultrasound reports. Fetal anatomic surveys were typically performed at approximately 20 weeks' gestation. Patients administered medication-assisted treatment (MAT) for opioid use disorder commonly had follow-up estimated fetal weight scans at approximately 32 weeks' gestation due to risks of intrauterine growth restriction. A retrospective review of ultrasound reports for three groups of patients was performed. The very-low-dose (VLD) group (127 patients) was taking ≤2 mg buprenorphine in their third trimester; the traditional dose (TD) group (103 patients) received higher-dose MAT that was consistent with current recommendations. The control group, no buprenorphine use, included 212 patients. One-way analysis of variance and Tukey's multiple comparison tests were used for statistical analysis. The effect size was measured using ω² [Formula: see text].

At the initial anatomy scan, no significant differences between groups were observed for head circumferences. By the third trimester growth scan, TD fetuses had significantly smaller head circumference percentiles compared with controls (P = 0.045). The estimated fetal weight percentile was lower in both buprenorphine groups compared with controls (VLD group vs controls, P = 0.021; TD group vs controls, P = 0.006), with TD fetuses showing the largest difference. Although TD head circumference percentiles were different from the controls, no significant differences were observed between the VLD group and either the TD group or controls for head circumference percentiles.

Previous studies have shown decreased head circumference in newborns in association with maternal MAT. This is the first study to provide ultrasound confirmation of decreased head circumference in fetuses exposed to buprenorphine. VLD buprenorphine may be associated with more favorable fetal growth measures compared with a TD. Interventions during pregnancy, including lowest effective dose treatment, may preserve fetal brain growth and improve long-term neurodevelopmental outcomes.