Impact of maternal age on the risk of perineal injury and obstetric anal sphincter injury in nulliparous women

OBJECTIVE: We aimed to evaluate the association between maternal age and the incidence of perineal injury including obstetric anal sphincter injuries (OASI) in nulliparous women. STUDY DESIGN: A retrospective cohort population-based study was conducted at a tertiary university-affiliated center from January 2011 to December 2020. This study included all nulliparous women with singleton pregnancies at term (37-41 weeks of gestation) in vertex and occiput anterior presentation who received epidural analgesia during labor. Exclusion criteria included stillbirth, chronic and obstetric maternal conditions (hypertension, diabetes mellitus, etc.), and deliveries complicated by instrumental vaginal delivery and episiotomy were excluded. The primary outcome was the incidence of perineal injury, defined as any spontaneous perineal tear, and/or OASI. RESULTS: During the study period, a total of 39,596 nulliparouss women delivered vaginally at our center. Of them 3410 (8.61%) met the inclusion criteria, with 843 (24.7%) in the 20-25 age group and 2567 (75.3%) in the 30-35 age group. Significant differences were observed between the two age groups in terms of ethnicity, maternal weight before pregnancy and at delivery, gestational glucose challenge test results, gestational age at delivery, duration of the second stage of labor, and birth weight. The incidences of perineal injury and OASI were significantly higher in the 20-25 age group compared to the 30-35 age group (perineal injuries: 58% vs. 53.2%; p value: 0.015; OASI: 0.9% vs 0.4%, p value: 0.04). In the multivariable logistic regression analysis assessing the association between maternal age and perineal injury, the overall odds ratio for perineal injury in relation to the younger age category was calculated as 1.22 (CI 1.03-1.44; p value: 0.023), indicating a higher risk of perineal injury in the 20-25 age group compared to the 30-35 age group. CONCLUSION: This study suggests that younger maternal age is independently associated with an increased risk of perineal injury and OASI among nulliparous women.