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

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.

Prediction of intrapartum caesarean section in vaginal breech birth: development of models for nulliparous and multiparous women.

OBJECTIVES: To develop prediction models for intrapartum caesarean section in vaginal breech birth. METHODS: This single-center cohort-study included 262 nulliparous and 230 multiparous women attempting vaginal breech birth. For both groups, we developed and (internally) validated three models for the prediction of intrapartum cesarean section. RESULTS: The prediction model for nulliparous women (AUC: 0.67) included epidural analgesia (aOR 2.14; p=0.01), maternal height (aOR 0.64 per 10 cm; p=0.08), birthweight ≥3.8 kg (aOR 2.45; p=0.03) and an interaction term describing the effect of OC if birthweight is ≥3.8 kg (aOR 0.24; p=0.04). An alternative model for nulliparous women which, instead of birthweight, included fetal abdominal circumference with a cut-off at 34 cm (aOR 1.93; p=0.04), showed similar performance (AUC: 0.68). The prediction model for multiparous women (AUC: 0.77) included prelabor rupture of membranes (aOR 0.31; p=0.03), epidural analgesia (aOR 2.42; p=0.07), maternal BMI (aOR 2.92 per 10 kg/m2; p=0.01) and maternal age (aOR 3.17 per decade; p=0.06). CONCLUSIONS: Our prediction models show the most relevant risk factors associated with intrapartum cesarean section in vaginal breech birth for both nulliparous and multiparous women. Importantly, this study clarifies the role of the OC by showing that this parameter is only associated with intrapartum cesarean section if birthweight is above 3.8 kg (or abdominal circumference is above 34 cm). Conversely, knowing the OC when the birthweight is less than 3.8 kg (or abdominal circumference is less than 34 cm) did not improve prediction of this surgical outcome.