The influence of the fetal leg position on the outcome in vaginally intended deliveries out of breech presentation at term - A FRABAT prospective cohort study.

Introduction: Vaginal delivery out of a breech presentation in pregnancies at term are being re-implemented into clinical practice. Still, recommendations regarding exclusion criteria leading to caesarean sections are based on expert opinions, not on evidence-based guidelines. The difference in perinatal outcome and course of delivery in births with babies in frank breech position and babies in incomplete or complete breech presentation never has been investigated in a large patient cohort.

Objective: To compare perinatal outcome of vaginally intended breech deliveries between births out of frank breech position and incomplete/complete breech presentation.

Design: Prospective cohort study.

Sample: 884 women at term with a singleton in frank breech presentation (FB) and 284 women with incomplete or complete breech presentation (CB) intending vaginal birth between January 2004 and December 2018.

Methods: Maternal and fetal outcome was compared between groups using Pearson's Chi Square test. Birth duration parameters were analysed using logistic regression.

Results: There were no differences in cesarean section rates (FB: 25.1%, CB 22.2%, p = 0.317). Short-term fetal morbidity did not differ between groups (FB: 2.5%, CB: 2.8%, p = 0.761). In vaginal deliveries the necessity to perform manual assistance was significantly more frequent in deliveries of infants in CB (FB: 39.9%, CB: 51.6%, p = 0.0013). Cord loops (FB: 10.1%, CB: 18.0%, p = 0.0004) and cesarean sections necessary because of cord prolapses (FB: 1.4%, CB 8.1%, p = 0.005) were significantly more often in deliveries with babies in CB.

Conclusion: This study provides evidence, that perinatal morbidity is not associated with the fetal leg posture in vaginally intended breech deliveries. The higher risk for the need of manual assistance during vaginal birth in deliveries of babies out of complete or incomplete breech presentation suggests that obstetrical departments re-implementing the vaginal breech in their repertoire might start with births of babies out of frank breech presentation.