Prevalence and Perinatal Outcomes Following In Utero Exposure to Prehospital Emergency Methoxyflurane: A 17-Year Retrospective Cohort Study

OBJECTIVE: To examine the prevalence of exposure and perinatal outcomes associated with in utero exposure to methoxyflurane. DESIGN, SETTING AND POPULATION: Whole-population ambulance data in Western Australia (WA) were linked to the statutory perinatal data collection to identify pregnant women transferred by ambulance between 2000 and 2016. The proportion of neonates in WA exposed to methoxyflurane, fentanyl or no analgesia during an ambulance transfer was calculated. Perinatal outcomes of pregnancies exposed to methoxyflurane (n=1579) were compared to those exposed to fentanyl (n=203) or no analgesia (n=10524) using multivariable logistic regression modelling. Perinatal outcomes were considered overall and by trimester of exposure. MAIN OUTCOME MEASURES: Primary outcomes were the prevalence of in utero methoxyflurane exposure and Apgar score on the day of delivery. RESULTS: In the study period, 0.4% of all neonates born in WA were exposed to methoxyflurane in utero. Methoxyflurane exposure on the day of delivery (n=657) was not associated with an increased likelihood of a low Apgar score at five minutes compared with no analgesia (n=2667) (OR 1.23, 95% CI 0.91-1.67). Whereas fentanyl exposure (n=22) was associated with an increased likelihood of low Apgar score compared with methoxyflurane (OR 3.67, 95% CI 1.18-11.48). CONCLUSIONS: Methoxyflurane is commonly used by ambulance services to treat pain in pregnant women in WA. While not recommended for use in pregnancy, pregnancies exposed to methoxyflurane did not have an increased risk of adverse perinatal outcomes in this study.