Resumo em Inglês:

SUMMARY OBJECTIVE: The aim of this study was to evaluate the relationship between intrapartum rectovaginal distance measured by transperineal ultrasonography and obstetric anal sphincter injury severity and second-stage labor duration in nulliparous women undergoing vaginal delivery. METHODS: This prospective cohort study was conducted at a tertiary referral center in Istanbul, between September 2021 and January 2022. Of 200 consecutive nulliparous women with singleton pregnancies at ≥37 weeks’ gestation, 148 who underwent vaginal delivery were included in the primary analysis. Intrapartum rectovaginal distance was measured in the midsagittal plane by 2D transperineal ultrasonography using a single operator during the inter-contraction rest period, at a fetal head station ranging from -1 to +1. Angle of progression and levator ani anteroposterior diameter were also recorded. Obstetric injury was graded per American College of Obstetricians and Gynecologists 2016 criteria; grade 3–4 laceration (severe obstetric anal sphincter injury) was the primary outcome. RESULTS: Severe obstetric anal sphincter injury occurred in 18 vaginal deliveries (12.2%). Rectovaginal distance was significantly shorter in women with severe obstetric anal sphincter injury (6.91±1.33 mm vs. 9.94±2.75 mm, p<0.001). Second-stage duration was longer with severe obstetric anal sphincter injury (125.8±6.5 vs. 91.3±18.0 min, p<0.001). Receiver operating characteristic analysis identified an rectovaginal distance cut-off of 8.1 mm (AUC=0.846; sensitivity 88.9%, specificity 80.8%). On multivariate logistic regression, rectovaginal distance (OR 0.516, 95%CI 0.373–0.713) and body mass index (OR 1.280, 95%CI 1.078–1.521) were independently associated with severe obstetric anal sphincter injury. CONCLUSION: Intrapartum rectovaginal distance measurement by transperineal ultrasonography is a noninvasive, readily obtainable parameter that independently predicts severe obstetric anal sphincter injury and may support individualized intrapartum risk stratification. Multicenter validation with larger samples is warranted.