Placental aromatase expression decreased in severe neonatal opioid withdrawal syndrome

<b>Background:</b> Severe neonatal opioid withdrawal syndrome (NOWS) cannot be predicted. Placental aromatase metabolizes both methadone and buprenorphine and may contribute to the severity of NOWS. <b>Objectives:</b> To determine whether placental aromatase mRNA expression differs in methadone- or buprenorphine-exposed placentas and is associated with NOWS severity. <b>Study design:</b> Prospective multicenter observational cohort study from July 2016 to December 2017. Inclusion: pregnant, ≥18 years old, singleton fetus, nonanomalous, ≥34 weeks at delivery, documented methadone or buprenorphine use. Exclusion: declined sample collection. Severe NOWS is defined as three consecutive Finnegan scores ≥8 or sum of three consecutive scores ≥24 within 72 hours of birth. Finnegan scoring was correlated with placental mRNA expression and compared to umbilical cord drug and metabolite levels. Data were analyzed using descriptive, parametric, and nonparametric statistics and regression analysis. <i>p</i>-Value <b>Results:</b> Thirty-eight out of 45 (84%) patients were included. Methadone and buprenorphine were used by 29/38 (76%) and 9/38 (24%) of patients, respectively. 19/38 (50%) infants had severe NOWS. Placental aromatase/actin mRNA expression was significantly lower in the placentas of infants with severe NOWS (<i>p</i> = .04). Mean umbilical cord 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP)/methadone ratios were significantly higher in infants with severe NOWS (<i>p</i> = .03). Placental aromatase mRNA expression was weakly to moderately correlated with umbilical cord methadone, buprenorphine, and their metabolite concentrations (<i>r</i> = 0.4–0.8). <b>Conclusion:</b> Placental aromatase mRNA expression was lower and umbilical cord EDDP/methadone ratios were higher in infants with severe NOWS. Additional investigation of placental aromatase in methadone- and buprenorphine-exposed pregnancies is needed.