The following is a summary of “Fentanyl in the labor epidural impacts the results of intrapartum and postpartum maternal and neonatal toxicology tests,” published in the JUNE 2023 issue of Obstetrics and Gynecology by Siegel, et al.

The impact of administering fentanyl through a labor epidural on peripartum individuals and its potential to cause positive urine toxicology tests were poorly understood. For a study, researchers sought to quantify the occurrence of positive maternal and neonatal urine toxicology tests due to neuraxial fentanyl used in labor neuraxial analgesia.

They conducted a prospective cohort study with pregnant participants planning a vaginal delivery with neuraxial analgesia. Exclusion criteria included a substance use disorder, hypertension, or renal/liver disease history. Urine samples were collected from mothers and neonates before, during, and after labor. Fentanyl testing was performed using two common methods: immunoassay and liquid chromatography with tandem mass spectrometric detection.

A total of 33 maternal-infant dyads were included, resulting in 178 urine specimens. Before initiating neuraxial analgesia, all maternal specimens tested negative for fentanyl using liquid chromatography with tandem mass spectrometric analysis and immunoassay. During labor, 26 of 30 (76.7%) participants showed positive results for fentanyl or its metabolites using liquid chromatography with tandem mass spectrometry, and 12 of 30 (40%) had positive immunoassay results. In postpartum, 19 of 21 (90.5%) participants had positive liquid chromatographs with tandem mass spectrometric results, and 13 of 21 (61.9%) had positive immunoassay results. Among the neonatal specimens, 10 (76.9%) tested positive using liquid chromatography with tandem mass spectrometry, with the last positive result observed 29 hours and 50 minutes after delivery.

Neuraxial fentanyl used for labor analgesia may lead to positive toxicology tests in mothers and neonates at different times after epidural initiation and cessation, varying rates depending on the testing method used. Caution is necessary when interpreting toxicology test results in individuals who received neuraxial analgesia to avoid false assumptions about nonprescribed fentanyl use.

Source: ajog.org/article/S0002-9378(22)02185-8/fulltext