Predelivery sonographic predictors of obstetric anal sphincter injury among nulliparous women

Objective: Data available at admission to delivery of nulliparous has rarely been investigated for prediction of obstetric anal sphincter injury (OASI). The aim of the present study was to study risk factors for OASI in nulliparous based on information available at admission. Methods: A retrospective study of all nulliparous women undergoing labor, during March 2011 to January 2021 was performed. We compared women with OASI following delivery to those without by univariate and multivariable regression. Results: A total of 30 262 deliveries were included and 4181 (13.4%) of those were delivered by an emergent cesarean delivery. OASI followed 453 (1.5%) deliveries. Women in the OASI group were younger 29 ± 4.4 versus 30 ± 4.8, P = 0.001. In a multivariable regression analysis, higher sonographic estimated fetal weight was positively associated with OASI occurrence (aOR, 95% CI: 1.13 [1.00–1.29]). Maternal age was inversely associated with OASI occurrence (adjusted odds ratio [aOR], 95% confidence interval [CI] 0.95 [0.92–0.97]). Conclusion: Sonographic fetal weight estimation is an independent risk factor for OASI occurrence that may be available at admission for delivery among nulliparous women.