Fentanyl in the Labor Epidural Impacts the Results of Intrapartum and Postpartum Maternal and Neonatal Toxicology Tests

Published:November 22, 2022DOI:
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      A positive urine fentanyl toxicology test may have significant consequences for peripartum individuals, yet the extent to which fentanyl in a labor epidural may lead to such a positive test is poorly characterized.


      To quantify the extent to which neuraxial fentanyl in labor neuraxial analgesia can lead to a positive peripartum maternal or neonatal urine toxicology test.

      Study Design

      We performed a prospective cohort study of pregnant participants planning a vaginal delivery with neuraxial analgesia. Participants with a history of substance use disorder, hypertension, renal or liver disease were excluded. A urine sample was collected prior to initiation of neuraxial analgesia, each time the bladder was emptied in labor, and up to four times postpartum. Neonatal urine was collected once. Urine fentanyl testing was performed with two common toxicology testing methods: immunoassay and Liquid-Chromatography with Tandem Mass Spectrometric detection (LC-MS/MS).


      33 maternal-infant dyads yielded a total of 178 urine specimens. All maternal specimens were negative for fentanyl on LC-MS/MS and immunoassay prior to initiation of neuraxial analgesia. Intrapartum, 26/30 (76.7%) of participants had positive LC-MS/MS for fentanyl or its metabolites, and 12/30 (40%) participants had positive immunoassays. Postpartum, 19/21 (90.5%) participants had positive LC-MS/MS, and 13/21 (61.9%) had a positive immunoassay. Of the 13 neonatal specimens collected, 10 (76.9%) were positive on LC-MS/MS, the last of which remained positive 29 hours and 50 minutes after delivery.


      Neuraxial fentanyl for labor analgesia may lead to positive maternal and neonatal toxicology tests at various times after epidural initiation and cessation and at different rates depending on the testing method used. Caution should be used in interpreting toxicology test results in individuals who receive neuraxial analgesia to avoid false assumptions of non-prescribed use.


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