Ultrasound assessment of the anovaginal distance as a predictor of obstetric perineal tears

Abstract

Background: Vaginal delivery is an important event in women’s life. It has a great impact on maternal health and efforts are directed towards safe vaginal delivery. Perineal tears cause great distress to laboring women. Objective: to determine the role of the anovaginal distance in the prediction of perineal tears in primiparous women.Study design: This prospective observational study was conducted at the labor and delivery ward at Suez Canal University hospital from June 2021 to December 2022. We recruited primiparous women attending for delivery at the labor ward following predetermined inclusion and exclusion criteria. At 36 weeks of gestation, the recruited women had transvaginal ultrasound for evaluation of the anovaginal distance. Intrapartum evaluation included nature of labor (spontaneous or induced), gestational age, duration of the first stage of labor, duration of the second stage of labor, state of the membranes, the number of vaginal examinations, and fetal biometry.Results: The mean age of the studied population was 25.52 ± 3.84 years. The mean BMI was 22.95 ± 1.12. The anovaginal distance was 15.33 ± 2.45 mm. Perineal tears occurred in 39/102 (38.2%) patients. There was no significant difference in the anovaginal distance between both groups (p value 0.834). A decrease in the anovaginal distance and smaller gestational age at birth predicted the occurrence of perineal tears significantly (p value 0.037 and 0.006, respectively). ROC curve determined a cut off value of 13.1mm for the AVD, below which perineal tears would occur with a sensitivity of 25.64% and a specificity of 88.89%. Conclusions: A short anovaginal distance predicted the occurrence of perineal tears significantly.