Mechanics of vaginal breech birth: Factors influencing obstetric maneuver rate, duration of active second stage of labor, and neonatal outcome.

ABSTRACT

BACKGROUND: We investigated possible parameters that could predict the need for obstetric maneuvers, the duration of the active second stage of labor (i.e., the duration of active pushing), and short-term neonatal outcome in vaginal breech births. MATERIALS AND METHODS: We performed a retrospective analysis of 268 successful singleton vaginal breech births in women without previous vaginal births from January 2015 to August 2022. Multivariable regression was used to investigate associations between maternal and fetal characteristics (including antepartum magnetic resonance (MR) pelvimetry) with obstetric maneuvers, the duration of active second stage of labor, pH values, and admission to the neonatal unit. Models for the prediction of obstetric maneuvers were built and internally validated. RESULTS: Obstetric maneuvers were performed in a total of 130 women (48.5%). A total of 32 neonates (11.9%) had to be admitted to the neonatal unit. The intertuberous distance (ITD) (p < 0.001), epidural analgesia (p < 0.001), and birthweight (p = 0.026) were associated with the duration of active second stage of labor. ITD (p = 0.028) and birthweight (p = 0.011) were also independently associated with admission to the neonatal unit, while pH values below 7.10 dropped significantly (p = 0.0034) if ITD was ≥13 cm. Furthermore, ITD (p < 0.001) and biparietal diameter (p = 0.002) were independent predictors for obstetric maneuvers. CONCLUSIONS: ITD is independently associated with the duration of active second stage of labor. Thus, it can predict suboptimal birth mechanics in the last stage of birth, which may lead to the need for obstetric maneuvers, lower arterial pH values, and admission to the neonatal unit. Consequently, MR pelvimetry gives additional information for practitioners and birthing people preferring a vaginal breech birth.