Impact of third- and fourth-degree perineal tears at first birth on subsequent pregnancy outcomes: a cohort study.

OBJECTIVE: To investigate, among women who have had a third- or fourth-degree perineal tear, the mode of delivery in subsequent pregnancies as well as the recurrence rate of third- or fourth-degree tears. DESIGN: A retrospective cohort study of deliveries using a national administrative database. SETTING: The English National Health Service between 1 April 2004 and 31 March 2012. POPULATION: A total of 639,402 primiparous women who had a singleton, term, vaginal live birth between April 2004 and March 2011, and a second birth before April 2012. METHODS: Multivariable logistic regression models were used to estimate odds ratios, adjusted for other risk factors. MAIN OUTCOME MEASURES: Mode of delivery and recurrence of tears at second birth. RESULTS: The rate of elective caesarean at second birth was 24.2% for women with a third- or fourth-degree tear at first birth, and 1.5% for women without (adjusted odds ratio, aOR 18.3, 95% confidence interval, 95% CI 16.4-20.4). Among women who had a vaginal delivery at second birth, the rate of third- or fourth-degree tears was 7.2% for women with a third- or fourth-degree tear at first birth, compared with 1.3% for women without (aOR 5.5, 95% CI 5.2-5.9). CONCLUSIONS: The risk of a severe perineal tear is increased five-fold in women who had a third- or fourth-degree tear in their first delivery. This increased risk should be taken into account when decisions about mode of delivery are made.