Transperineal ultrasound has become the gold standard for diagnosis of tears of the levator ani muscle from its bony insertion, so called avulsion. Levator avulsion is considered a missing link between childbirth and prolapse development. 

A decrease of avulsion-rates within the first 6 months after first delivery has previously been described (1). The process of recovery but also false positive diagnosis due to hematoma and tissue edema are discussed as explanations for this reported decrease.

Whereas the effect of subsequent deliveries on levator avulsion has been studied previously (2), little is known about the levator anatomy in women with sonographically improved muscle (nonpersistent avulsion) within the first year after delivery in longer follow-up. If recovery takes place, the sonographically improved muscle might not have its full functional reserve and subsequent deliveries and advancing age might worsen levator avulsion status again. 

The aim of the study was to assess levator avulsion 8 years after first delivery according to avulsion status (no avulsion, nonpersistent avulsion, persistent avulsion) within the first year after first delivery.

This is a single center longitudinal cohort study. Primiparas, who delivered one child after more than 32 weeks of gestation were included 6 weeks after first delivery. Exclusion criteria was pelvic floor surgery during the follow-up. Participants underwent transperineal ultrasound of the pelvic floor at 6 weeks, 6 months, one year and 8 years after first delivery. Levator avulsion was diagnosed by tomographic ultrasound imaging. Avulsion was defined according to Dietz et al., when an abnormal muscle insertion was present in all three central slices (3). Great care was taken to define the correct reference slice at the plane of minimal hiatal dimensions, showing the most inferior aspect of the symphyseal gap, with the pubic rami appearing hyperechoic.

Study groups were defined according to avulsion status within the first year after first delivery: (no-avulsion group= normal levator insertion or abnormal muscle insertion in less than three central slices at all time points; nonpersistent avulsion group= avulsion at 6 weeks but normal levator insertion or abnormal muscle insertion in less than three central slices at follow-up within the first year after first delivery; persistent avulsion group= avulsion at all time points). When ultrasound assessment was missing one year postpartum, ultrasound assessment 6 months postpartum was used. The evaluation of levator avulsion was performed by two investigators with good to excellent inter- and intra-rater agreement for detecting an avulsion (kappa 0.79). Demographics and delivery data at first delivery were obtained from the women`s electronic hospital records. Information on subsequent deliveries was obtained at the 8-year follow-up. The investigators were blinded to previous ultrasound findings, participants’ demographic data and obstetric histories.

In this study 321 participants were included 6 weeks after first delivery. One participant was excluded due to pelvic floor surgery during the follow-up. 206 participants (64%) attended the 8-year follow-up. Out of the 206 participants with ultrasound examination 6 weeks and 8 years after first delivery, 162 participants (78.6%) were allocated to the no-avulsion group, 16 participants (7.8%) to the nonpersistent avulsion group and 20 participants (9.7%) to the persistent avulsion group. Eight participants with normal levator insertion or abnormal muscle insertion in less than three central slices at 6 weeks had missing ultrasound follow-up within one year after first delivery. In all participants avulsion status improved or remained unchanged on ultrasound within the first year after delivery. Eight years after first delivery 26 participants (12.6%) were diagnosed with levator avulsion. No participant with normal levator insertion at all time points within the first year after first delivery was diagnosed with an avulsion 8 years later. In the nonpersistent avulsion group 5 out of 16 participants (31%) had an avulsion 8 years after first delivery (Figure 1), in 3 of them the levator insertion was evaluated as normal at one year follow-up, in 2 participants abnormal muscle insertion in less than three central slices was diagnosed at one year follow-up. All participants with persistent avulsion had an avulsion 8 years after first delivery (Figure 1).

Background and obstetric data from the study groups is presented in Table 1. The majority of our study population had subsequent vaginal deliveries after first delivery. Four out of 5 participants from the nonpersistent avulsion group, and the one participant with abnormal muscle insertion in less than three central slices 6 weeks who were diagnosed with avulsion at 8-year follow-up had subsequent vaginal deliveries. No participant with vaginal delivery after cesarean section had an avulsion at 8-year follow-up.

Previous studies have shown that levator avulsion almost exclusively occur during the first vaginal delivery, new diagnosed avulsion after subsequent vaginal delivery is rare (2). In our study, we found 5 participants with avulsion at 8-year follow-up in the nonpersistent avulsion group. All participants in the nonpersistent avulsion had subsequent vaginal deliveries. On the other hand, no avulsion was found in participants in the no-avulsion group in the 8-year follow-up, despite high numbers of subsequent vaginal deliveries in this group. We interpret this as a confirmation, that the sonographic improvement within the first year does not reflect a completely restored muscle with normal function comparable to a non-injured levator muscle. Thereby, subsequent vaginal deliveries and ageing, may worsen avulsion status over time.

Levator avulsion status can worsen over time and after subsequent vaginal deliveries, one third of the participants in the nonpersistent avulsion group had an avulsion 8 years after first delivery. Participants with normal levator insertion at all time points within first year after first delivery were not diagnosed with avulsion 8 years later. All participants with persistent avulsion within the first year after first delivery had an avulsion at 8-year follow-up.

van Delft K, Thakar R, Sultan A, IntHout J, Kluivers K. The natural history of levator avulsion one year following childbirth: a prospective study. BJOG. 2014.
Horak TA, Guzman-Rojas RA, Shek KL, Dietz HP. Pelvic floor trauma: does the second baby matter? Ultrasound Obstet Gynecol. 2014;44(1):90-4.
Dietz HP, Bernardo MJ, Kirby A, Shek KL. Minimal criteria for the diagnosis of avulsion of the puborectalis muscle by tomographic ultrasound. International urogynecology journal. 2011;22(6):699-704.

Continence 7S1 (2023) 100720
DOI: 10.1016/j.cont.2023.100720