Limbic System Microstructure in Neonates With Antenatal Opioid Exposure

There is limited research examining the association of antenatal opioid exposure with neonatal brain microstructure, particularly within the limbic system, which contains high concentrations of opioid receptors. Prior studies investigating microstructural changes in major white matter tracts were underpowered and lacked matched controls.

To compare limbic system microstructure between neonates who were opioid exposed and unexposed.

This case-control study assessed diffusion tensor imaging of neonates enrolled in the Outcomes of Babies With Opioid Exposure (OBOE) study and scanned between August 2020 and December 2023 at 4 US sites. Participants were term neonates with antenatal exposure and unexposed controls. Data were analyzed from July 2024 to April 2026.

Neonates were antenatally exposed to methadone, buprenorphine, oxycodone, hydromorphone, fentanyl, hydrocodone, heroin, morphine, or some combination of these opioids.

The primary outcome was limbic system diffusion metric comparisons between neonates who were exposed and unexposed. Diffusion tensor imaging data in term neonates were acquired using harmonized protocols on Siemens and Philips 3T magnetic resonance imaging scanners, preprocessed using a neonatal-optimized pipeline, and analyzed. Using analysis of covariance, fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity were compared in the limbic system of neonates who were unexposed vs opioid exposed. In secondary, exploratory analyses, diffusion metrics in the limbic system were compared between subgroups of opioid exposure (methadone, buprenorphine, and other opioids) and controls. False discovery rate (FDR) was used to correct for multiple comparisons.

Among 201 enrolled neonates, 75 were unexposed (mean [SD] postmenstrual age, 42.76 [2.05] weeks; 45 male [60.0%]) and 126 were antenatally opioid exposed (mean [SD] postmenstrual age, 42.72 [2.06] weeks; 65 male [51.6%]), of which 79 were exposed to buprenorphine, 30 to methadone, and 14 to other opioids. Neonates who were opioid exposed showed a significantly lower mean diffusivity (mean difference [β] = -0.06 × 10-3 mm2/s [95% CI, -0.11 to -0.01 × 10-3 mm2/s]; FDR P = .04) and radial diffusivity (β = -0.07 × 10-3 mm2/s [95% CI, -0.12 to -0.02 × 10-3 mm2/s]; FDR P = .04) in the fornix. Secondary, exploratory analyses revealed buprenorphine-specific associations (eg, higher mean diffusivity in the left parahippocampal gyrus vs no opioid exposure: β = 0.02 × 10⁻3 mm2/s [95% CI, 0.00 to 0.04 × 10⁻3 mm2/s]) and other opioid-specific associations (eg, higher fractional anisotropy in the left thalamus for other opioids vs unexposed: β = 0.01 [95% CI, 0.01 to 0.02]) in GM limbic system structures.

This study found altered limbic system microstructure, particularly in the fornix, in neonates with antenatal opioid exposure, and exploratory analyses showed different patterns of limbic system microstructure across opioid exposure subgroups. Clinical correlation is needed.