Nitrous oxide is widely used for labor analgesia. But, there is lack of data supporting the analgesic effectiveness of nitrous oxide for labor pain.

A retrospective descriptive study was conducted with an objective to investigate the characteristics of women who selected nitrous oxide as analgesia for labor pain. The study also evaluated the factors that predict conversion from nitrous oxide to labor neuraxial analgesia. This study reviewed the chart of 146 pregnant women who used nitrous oxide for analgesia during labor and delivery between September 2014 and September 2015.

Demographic, obstetric, and intrapartum characteristics of women were measured. Multivariable logistic regression was performed to discover factors which cause the conversion of nitrous oxide to neuraxial analgesia. Data are shown as n (%), median [IQR], adjusted relative risk (aRR), and 95% confidence intervals (CI) as relevant.

At the time of the study, about 146 women used nitrous oxide for labor analgesia (accounting for 3% of the total deliveries). It was examined that most of the women (71.9%) who used nitrous oxide were nulliparous, and over half (51.9%) preferred "nonmedical birth." The conversion rate to neuraxial blockade was 63.2%, compared to a collective institutional rate of 85.1% in women who did not use nitrous oxide.

Factors that were found to be associated with conversion from nitrous oxide to neuraxial blockade were labor induction (aRR = 2.0, CI 1.2–3.3) and labor augmentation (aRR = 1.7, CI 1.0–2.9). The study concludes that very few numbers of women opted to have nitrous oxide during labor, analgesia was minimal, and most converted to neuraxial analgesia. Women with induced and augmented labors should be advised about the increased possibility that they will convert to neuraxial analgesia.