External cephalic version: Success rates with and without nitrous oxide

Background: External cephalic version (ECV) is a technique used to reduce the incidence of cesarean deliveries due to malpresentation. Nitrous oxide is an inhaled analgesic that may be used for pain relief for women undergoing external cephalic version.Objective: To compare the conversion rate of non-cephalic to cephalic presentation in ECV with and without nitrous oxide.Study design: A retrospective cohort analysis was performed including all singleton, term gestation ECVs between January 2016 and June 2017 at a single institution. Multivariable logistic regression was used to compare women who had ECV with nitrous oxide versus ECV without nitrous oxide. The primary outcome was successful rate of conversion to cephalic presentation and the secondary outcome was the rate of vaginal delivery.Results: During the study period, 167 women underwent ECV: 77 with nitrous oxide and 90 without nitrous oxide. Of the 77 women who used nitrous oxide, 25 (32.5%) were successful and 17 of these women delivered vaginally (68%). Of the women who underwent ECV without nitrous oxide, 29 (32.2%) successfully converted and 21 of these delivered vaginally (72%). After controlling for confounders, the use of nitrous oxide had no clinically or statistically significant difference on ECV success rates (OR 1.08, 95% CI 0.52-2.23).Conclusion: Nitrous oxide does not seem to affect conversion rate to cephalic presentation in ECV. Further studies are needed to determine the impact of nitrous oxide on women's decision to undergo ECV and on patient satisfaction and tolerability.