Successive intra- and postpartum measurements of levator–urethra gap to establish timing of levator avulsion

Vaginal delivery is one of the most important risk factors for future pelvic floor dysfunction. Although modifiable risk factors for levator ani muscle (LAM) avulsion have been identified, the mechanism by which it is produced has not been described. Different researchers have hypothe sized that the lesion of the LAM could be due to bulging of the head of the fetus on the maternal perineum. Recently, a study carried out using three-dimensional (3D) intra partum transperineal ultrasound described that maximum distension of the levator hiatus area occurs when the fetal head is in the fourth plane of Hodge (vertex at station + 3 or + 4)1, which is the point at which the muscle seems to be most susceptible to trauma. We aimed to determine the changes in levator–urethra gap (LUG) measurements during descent of the fetal head and postpartum.