Fentanyl concentration in maternal and umbilical cord plasma following intranasal or subcutaneous administration in labour

Background: The effect that the route of maternal fentanyl administration has on placental transfer of drug to the neonate is not well studied. Plasma concentration ratios are an indicator of fetal exposure, relative to the mother. Methods: A cohort study (n=30) was conducted to measure fentanyl concentrations in maternal plasma, and arterial and venous cord blood, among women administered either intranasal or subcutaneous fentanyl for labour pain relief. Maternal and cord blood samples were collected within 30 min of birth to determine the fentanyl plasma concentration and to assess relative neonatal exposure. Neonatal outcomes were assessed by Apgar scores, need for resuscitation and nursery admission. Results: Thirty paired samples were obtained from healthy parturients with uncomplicated term pregnancies. Highest observed umbilical venous and arterial concentrations were 0.71 ng/mL and 0.56 ng/mL, respectively, and fetal to maternal fentanyl plasma concentration ratios ranged between 0.23 and 0.73, indicating low fetal exposure. While the total intranasal fentanyl dose administered was significantly higher than the subcutaneous fentanyl dose, this did not result in a higher fetal to maternal ratio. All neonates in both groups had 5-min Apgar scores >7, two neonates required short-term stimulation and oxygen (unrelated to fentanyl) and no neonate was admitted to the nursery. Conclusion: This study is the first to examine fetal and maternal fentanyl concentrations after subcutaneous administration. This research supports the safe use of fentanyl for labour analgesia for women.