Vaginal Birth After Caesarean Raises Risk of Perineal Tear

Vaginal birth after caesarean (VBAC) has been suggested to be associated with an increased risk of obstetric anal sphincter injury (compared with primiparous women who birth vaginally). However, prior studies have been small or have used outdated methodology. Therefore, Dr Anthea Lindquist and his team conducted a study to validate whether the risk of obstetric anal sphincter injury among women having their first VBAC is greater than that among primiparous women having a vaginal birth.

In a state-wide retrospective cohort study, the researchers included 130,000 births and compared the risk of a third-degree perinatal tear among first-time mums with those who birth vaginally after a prior cesarean. They examined covariates using logistic regression for categorical data and the Wilcoxon rank-sum test for continuous data. They used multiple imputations to handle missing data and performed stat analysis using regression adjustment and stata 16 multiple imputation and suite of effects commands.

Key findings of the study:

• Upon analysis, the researchers found that women having a VBAC (n = 5429) were significantly more likely than primiparous women (n = 123 353) to sustain a third- or fourth-degree tear during vaginal birth (7.1 versus 5.7%).
• After adjustment for a mode of birth, body mass index, maternal age, infant birth weight, episiotomy and epidural, they observed a 21% increased risk of severe perineal injury (RR 1.21).

The authors concluded, "Women having their first VBAC have a significantly increased risk of sustaining a third- or fourth-degree tear, compared with primiparous women having a vaginal birth. Patient counselling and professional guidelines should reflect this increased risk."

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DOI: https://doi.org/10.1111/1471-0528.17063