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.

Intrapartum ultrasound at the initiation of the active second stage of labor predicts spontaneous vaginal delivery

BACKGROUND

Longer duration of active pushing during labor is associated with a higher rate of operative delivery and an increased risk of maternal and neonatal complications. Although immediate pushing at complete dilatation is associated with lower rates of chorioamnionitis and postpartum hemorrhage, it is also associated with a longer duration of pushing.

OBJECTIVE

This study aimed to evaluate whether fetal head station and position, as assessed by ultrasound at the beginning of the pushing process, can predict the mode of delivery and duration of pushing in nulliparous women.

STUDY DESIGN

This prospective observational study included nulliparous women with neuraxial analgesia and complete cervical dilatation. The following sonographic parameters were assessed just before the beginning of the pushing process, at rest, and while pushing during contraction: head position, angle of progression, head-perineum distance, and head-symphysis distance. The change between rest and pushing was designated as delta angle of progression, delta head-perineum distance, and delta head-symphysis distance. The sonographic measurements and fetal head station assessed by vaginal examination were compared between women who had a spontaneous vaginal delivery to those who underwent an operative delivery, and between those who pushed for more or less than 1 hour.

RESULTS

Of the 197 women included in this study, 166 (84.3%) had a spontaneous vaginal delivery, 31 (15.7%) had an operative delivery, 23 (11.6%) had a vacuum delivery, and 8 (4.0%) had a cesarean delivery. Spontaneous vaginal delivery and shorter duration of pushing (less than an hour) were significantly more common with a nonocciput posterior position (10.6% vs 47.3%; P<.005), a wider angle of progression, a shorter head-perineum distance and head-symphysis distance (both during rest and while pushing), and a lower fetal head station as assessed by digital vaginal examination. However, a logistic regression model revealed that only the angle of progression at rest and the delta angle of progression were independently associated with a spontaneous vaginal delivery with an area under the curve of 0.82 (95% confidence interval, 0.76-0.87; P<.0001) and 0.75 (95% confidence interval, 0.67-0.79; P<.0001), respectively.

CONCLUSION

Ultrasound performed at the beginning of the active second stage of labor can assist in predicting the mode of delivery and duration of pushing and perform better than the traditional digital examination, with the angle of progression at rest and delta angle of progression being the best predictors.