Does the fetal head station and position affect the pelvic floor muscles in labour? A prospective study using 3 dimensional transperineal ultrasound

This is the first study to evaluate how the fetal head station and position affect the LAM after active second stage of labour. There is a 25 % increase in AP diameter and a doubling of the hiatal area as the head descends from station -1 to +2. LAM avulsions are known to occur following a vaginal birth, and this study demonstrates that LAM avulsions do not occur until the birth of the head. It also highlights that despite pushing in the active second stage of labour, an unsuccessful vaginal delivery followed by CS is not associated with a LAM avulsion. This information will be useful to counsel women regarding mode of delivery.