The evolution of levator ani muscle trauma over the first 9 months after vaginal birth

The objective was to investigate the evolution of levator ani muscle (LAM) trauma over the first 9 months after birth and to evaluate their agreement between different assessment periods.

From March 2017 to April 2019 we prospectively evaluated LAM states (intact, hematoma, partial or complete avulsion) of primiparous women after vaginal birth by using 4D translabial ultrasound (TLUS) at three different assessment periods. All women were examined 1-4 days (A1) and 6-10 weeks (A2) postpartum, and women with a trauma additionally 6-9 months postpartum (A3). Cohen's Kappa analysis was performed to evaluate the test agreement between the assessment periods.

Thirty-two percent of the women at A1 had a LAM trauma and 24% at A2. The higher number of LAM injuries at A1 can be explained by hematomas (14%), of which 51% spontaneously resolved at A2, 35% revealed themselves as partial, and 12% as complete avulsions. At A3, we observed anatomical improvement from complete to partial avulsions (23%) and few partial avulsions changed into an intact LAM (3%); none of the complete avulsions changed into an intact LAM. The agreement of 4D TLUS between A1 and A2 was moderate to good (0.64 for the right-sided LAM/0.60 for the left-sided LAM) and between A2 and A3 good to very good (0.76 right-sided/0.84 left-sided).

Levator ani muscle trauma can reliably be diagnosed during all assessment periods. However, the agreement between A1 and A2 was only moderate to good. This can be explained by hematomas inside the LAM that were only observed early postpartum. We observed some anatomical improvement at A3, but no complete avulsion improved to an intact LAM.