Risk factors for obstetric anal sphincter injury among adolescents.

Objective: Data regarding the risk factors for obstetrical anal sphincter injury (OASI) among nulliparous adolescent women are scarce. We aimed to evaluate these risk factors.

Study Design: A retrospective case-control study of nulliparous women aged ≤ 21 who delivered vaginally between 3/2011 and 6/2021. Maternal and intrapartum characteristics were compared between OASI and no-OASI groups.

Results: Of 1,342 deliveries, 22 (1.6%) cases of OASI were diagnosed. Maternal anthropometric and demographic characteristics did not vary between study groups. Gestational comorbidity (diabetic and hypertensive disorders) was associated with an increased risk for an OASI [OR 95% CI 3.1 (1.1-8.6)]. The rate of prolonged second stage was associated with an OASI [OR 95% CI 2.5 (1.1-6.5)]. The mode of delivery was similar in both groups. There were no forceps deliveries in the OASI group. Birthweight and the proportion of newborns weighing more than 4,000 g were similar in both study groups. All sonographic biometric measurements did not vary between study groups. Women with an OASI had higher rate of blood transfusion [OR 95% CI 11.4 (3.1-42.0)]. In a multivariable regression analysis, including birthweight, vacuum assisted delivery, prolonged second stage and gestational comorbidity - gestational comorbidity was the only independent factor associated with the occurrence of an OASI [adjusted OR 95% CI 2.9 (1.05-8.17)].

Conclusion: Gestational comorbidity is the only predictor of OASI among nulliparous adolescent women.