Adding Insult to Injury: Levator Ani Avulsion in Women With Obstetric Anal Sphincter Injuries

Obstetric anal sphincter injuries (OASIS) and levator ani avulsion (LA) are 2 of the more widely studied neuromuscular birth injuries. Although they may occur together, sometimes they do not. Route of delivery has been suggested as one of the factors that may increase the risk of LA in women with OASIS. However, this has been difficult to study because the number of women with OASIS in studies of LA has been small. The aim of this study is to compare the rate of LA in women with OASIS who undergo forceps-assisted delivery versus spontaneous vaginal delivery. This was a prospective study of adult women with OASIS recruited at a single hospital between March 2016 and June 2017. Women who had wound breakdown/infection or who underwent vacuum-assisted delivery were excluded. Women were enrolled 1 to 2 weeks postpartum. At their initial visit, they underwent an ultrasound examination to identify LA avulsion and completed questionnaires for pelvic floor disorders symptoms. The primary outcome was LA avulsion on ultrasound. Secondary ultrasound outcomes were anteroposterior hiatal diameter, levator hiatus, and levator-urethra gap. A total of 62 women with OASIS were included in the analysis-30 who delivered spontaneously and 32 who underwent forceps-assisted delivery. Significantly more women who underwent forceps-assisted delivery had LA avulsion than those who delivered spontaneously ( 21/32 [65.6%] vs 8/30 [26.7%], P = 0.004). Independent associations with LA avulsion were observed for forceps-assisted delivery (odds ratio [OR], 5.9; 95% confidence interval [ CI], 1.5-24.5; P = 0.014) and labor duration (OR, 1.01; 95% CI, 1.0-1.02; P = 0.022) after controlling for variables. There was a larger levator- urethra gap bilaterally in the forceps-assisted delivery group than the spontaneous delivery group (left, P = 0.012; right, P = 0.016). No differences were observed in the hiatal area ( P = 0.84) and anteroposterior diameter ( P = 0.86). A total of 52 of the 62 (83%) women completed the pelvic floor questionnaires at both baseline and 13 weeks postpartum, with median scores generally remaining stable or improving over this period. After controlling for variables, LA avulsion was independently associated with persistent symptoms of anal incontinence at 13 weeks postpartum ( P = 0.02). There was no association between delivery type changes in symptoms of anal incontinence ( P = 0.14). In conclusion, there was a 6-fold increased risk of LA avulsion in women with OASIS who underwent forceps-assisted delivery compared with those who delivered spontaneously. Women with OASIS and LA avulsion were also more likely to have persistent symptoms of anal incontinence.