Objective  To investigate risk factors of severe perineal tears, so as to provide scientific evidence for preventing severe perineal tears, improve the quality of midwifery techniques and promote postpartum recovery.

Methods  From January 2016 to April 2022, 16 women with severe perineal tears (degree ⅲ and iv) who delivered vaginally in a grade A tertiary obstetrical and gynecological hospital were recruited as case group. At the same time, 64 parturients without severe perineal tears (0, ⅰ, ⅱ degrees) were recruited as control group according to age ( ± 5 years) and delivery date ( ± 42 days) with a 1:4 matched case-control study design. The risk factors of severe perineal tears during delivery were analyzed by univariate and multivariate conditional logistic regression analysis.

Results  The maternal age, height, gestational weeks at delivery, and educational background were comparable between 2 groups (all P > 0.05). Univariate analysis indicated that there were statistically significant differences between 2 groups in terms of being primipara, history of cervical surgery, abdominal circumference, weight gain during pregnancy, pre-pregnancy body mass index, duration of the second stage of labor, and being shoulder dystocia (all P < 0.05). Logistic regression analysis showed primipara (P = 0.043, OR = 43.212, 95% CI: 1.120 − 1 667.865), history of cervical surgery (P = 0.023, OR = 25.194, 95% CI: 1.548 − 410.123), excessive weight gain during pregnancy (P = 0.021, OR = 15.020, 95% CI: 1.518 − 148.614) and pre-pregnancy obesity (P = 0.030, OR = 869.382, 95% CI: 1.900 − 397 823.015) were independent risk factors associated with severe perineal tears in vaginal delivery.

Conclusion  Primipara, history of cervical surgery, excessive weight gain during pregnancy and pre-pregnancy obesity have higher risk of severe perineal tears during childbirth. Maternity settings should emphasize on providing standardized pre-pregnancy care and weight management during pregnancy, especially for primiparas, and implement correct labor process management to prevent the occurrence of severe perineal tears during childbirth.