Levator avulsion and vaginal parity: do subsequent vaginal births matter?

Tears of the levator ani muscle are common after vaginal birth and associated with pelvic organ prolapse (POP). Although such trauma is usually attributed to the first vaginal birth, epidemiological evidence suggests an additional effect of subsequent vaginal deliveries. Our hypothesis was: "The prevalence of avulsion increases with the number of vaginal births".

We conducted a retrospective cohort study in patients who presented to a tertiary urogynaecology clinic. Assessment included a physician-directed interview, POP-Q and 4D translabial ultrasound (TLUS), supine, after voiding, at rest, on maximum pelvic floor muscle contraction (PFMC) and Valsalva. Offline analysis of levator integrity was undertaken by tomographic imaging (TUI) at a later date, blinded against all other data.

A total of 1,124 patients had been seen between 1 January 2014 and 30 June 2016, on average 33 (0.32-69.7) years after their first birth. Mean age was 56 (19-90) years. 1,012 (90%) were vaginally parous with a median vaginal parity of 2 (1-8). On TUI, avulsion was diagnosed in 257 (23%) women, all of whom were vaginally parous. On univariate analysis, there was no significant difference in the prevalence of avulsion on comparing vaginally primiparous and multiparous women (P = 0.6), nor was there any difference between vaginal parity groups (one, two, three, and ≥4 births; p = 0.7). This remained true after controlling for potential confounding factors using multivariate regression (p = 0.6).

There was no significant difference in the prevalence of avulsion between vaginally primiparous and multiparous women. Vaginal deliveries after a first vaginal birth are unlikely to cause avulsion.