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A Retrospective Cohort Analysis of the Association Between the use of Nitrous Oxide in Labor and Delivery and Maternal Outcomes
Abstract Number: F1B-2
Abstract Type: Original Research
Background: Most studies evaluating labor analgesia focus on the safety epidural analgesia and opioids. This leaves a gap in the literature regarding the use of inhaled nitrous oxide (N2O) on maternal outcomes.
Objective: To determine the association between inhaled 50:50 nitrous oxide and oxygen during labor and delivery for pain management and maternal outcomes.
Methods: This study is a retrospective cohort including deliveries of singleton, term fetuses from 1995-2016 recorded in the Perinatal Database; planned cesarean deliveries (CD) were excluded. Three exposure groups were defined: 1) N2O only, 2) epidural only, 3) N2O and epidural combined. Maternal outcomes included postpartum hemorrhage (PPH), shoulder dystocia, maternal postpartum length of stay in hospital >72 hours, CD, instrumental delivery, prolonged second stage labor, and breastfeeding status at discharge. Logistic regression was used to estimate odds ratios (OR) with adjustment for confounding variables including maternal age, maternal weight, neighborhood-level income, smoking status, pre-existing and/or gestational diabetes or hypertension, pre-eclampsia, opioid use during labor/delivery, and birthweight.
Results: Of all recorded deliveries, 146,014 (primiparous N=69,222, multiparous N=76,792) met inclusion criteria. In primiparous and multiparous women, the use of N2O alone was associated with increased odds of PPH (OR 1.1, 95%CI, 1.0 to 1.3; and OR 1.2, 95%CI, 1.1 to 1.4), shoulder dystocia (OR 1.2, 95%CI, 1.0 to 1.5; and OR 1.4, 95%CI, 1.2 to 1.6), and breastfeeding status (OR 1.2, 95%CI, 1.1 to 1.3; and OR 1.2, 95%CI, 1.1-1.2). In primiparous women, N2O alone was associated with decreased odds of maternal postpartum length of stay >72 hours (OR 0.7, 95%CI, 0.6 to 0.8), CD (OR 0.3, 95%CI, 0.28 to 0.34), and prolonged second stage of labor (OR 0.8, 95%CI, 0.6 to 0.9). In primiparous women, combined use of N2O and epidural was associated with increased odds of PPH (OR 1.3, 95%CI, 1.2 to 1.5), CD (OR 1.6, 95%CI, 1.5 to 1.7), instrumental delivery (OR 2.3, 95%CI, 2.1 to 2.5), prolonged second stage labor (OR 8.9, 95%CI, 7.8 to 10.0), and breastfeeding status (OR 1.5, 95%CI, 1.4 to 1.6). In multiparous women, the use of N2O alone was associated with decreased odds of postpartum length of stay >72 hours (OR 0.6, 95%CI, 0.59 to 0.7) and CD (OR 0.2, 95%CI, 0.16 to 0.22). In multiparous women, the use of N2O combined with epidural was associated with increased odds of CD (OR 1.5, 95%CI, 1.3 to 1.7), instrumental delivery (OR 3.0, 95%CI, 2.6-3.4), prolonged second stage of labor (OR 9.3, 95%CI, 8.3 to 10.4), and breastfeeding status (OR 1.3, 95%CI, 1.2 to 1.5).
Conclusions: The use of N2O was associated with reduced odds of some adverse maternal outcomes in this population and increased odds of other outcomes. These mixed results and potential residual confounding by indication demonstrate the need of further research in this area in the form of randomized controlled trials.