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Effect of Chronic Maternal Methadone Therapy on Intrapartum Fetal Heart Rate Patterns

Obstetrics and Gynecology, Maternal-Fetal Medicine Division, University of New Mexico, 2211 Lomas Blvd., MSC 10 5580, Albuquerque, NM 87111 wramirez{at}salud.unm.edu

Stephanie Flores, MD

Ron M. Schrader, PhD

Jaymi McKay, RN

William R. Rayburn, MD

Department of Obstetrics and Gynecology, Maternal-Fetal Medicine Division, University of New Mexico, Albuquerque, New Mexico, USA

Objective: Treatent of matemal opioid dependence with methadone is associated with a delay in fetal heart rate (FHR) accelerations in nonstress tests. The objective of this investgation was to determine the effect of methadone maintenance therapy on intrapartum FHR patterns.

Methods: This retrospective cohort study compared intrapartum FHR tracings from 56 methadone-treated patients 36 weeks gestation with a control group of nonsubstance using patients matched for maternal age, parity, gestational age, and ethnicity. Blinded FHR interpretation included the recording of baseline, variability, accelerations, and late or severe variable decelerations. The 8-point FHR scoring system was based on the National Institute of Child Health and Human Development Research Planning Workshop guidelines. We considered a 25% reduction in the score during the latent phase to be significant.

Results: The median maintenance dose of methadone was 70 mg daily, with a range between 20 mg and 130 mg. Each patient tested negative for other substances on urine screening before admission. The significantly lower FHR score in the methadone group (mean difference, 1.4; 95% confidence interval, 1.1 to 1.7) was attributed to a lower baseline (P <.05), less moderate or marked variability (P <.01), and a lower proportion of accelerations during the first stage of labor (P <.01). A higher proportion of methadone-exposed fetues had late or severe variable decelerations in the second stage (44.2% vs 22.9%; P <.03). Analgesic needs, operative vaginal or cesarean delivery rates, and Apgar scores less than 7 at 1 and 5 minutes were not significantly different between the two groups.

Conclusions: Chronic maternal methadone treatment affects intrapartum FHR patterns by reducing the variability, baseline, and proportion of accelerations during the first stage. These subtle drug-induced effects do not compromise intrapartum decision-making or immediate newborn adjustments.

Key Words: Methadone • fetal heart rate • substance use • intrapartum monitoring

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