This study was performed to determine the effect of a primary anal sphincter injury in the first vaginal delivery as a risk factor for recurrent anal sphincter injury in subsequent vaginal deliveries.
This is a population-based cohort study that used data from the California Office of Statewide Health Planning and Development. The study population (Lac First) was defined as women having their first singleton vaginal delivery between 1991 and 1995 complicated by an anal sphincter injury, with a second vaginal delivery between 1991 and 2004. These women were compared to a control group of women without anal sphincter injury (Nolac First) during the same time period. The primary outcome of interest was occurrence of an anal sphincter injury in the second vaginal delivery. Maternal demographics, obstetric and labor data, and fetal data were collected for the second delivery. Odds ratios for recurrent anal sphincter injury were calculated using multivariate logistic regression and were reported with 95% confidence interval.
A total of 375,278 women were identified with their first vaginal delivery between 1991-1995 and a second vaginal delivery before 2005. The Lac First group consisted of 43,583 (11.6%) women with an anal sphincter injury. During their second delivery, 2,648 (6.1%) had a recurrent anal sphincter injury. In contrast, in the Nolac First group, only 1.4% (4,697 of 331,695 women) were found to have anal sphincter injury at the time of their second delivery. The adjusted odds ratio for recurrent injury was 3.79 (95% CI 3.60-3.98). Variables significantly associated with recurrent anal sphincter injury at the time of second delivery were found to be increasing maternal age >40 (OR 1.34, 95% CI 1.14-1.58), fetal macrosomia >5000g (OR 9.92, 95% CI 7.44-13.22), operative deliveries with forceps (OR 4.69, 95% CI 3.77-5.82) and vacuum (OR 1.96, 95% CI 1.74-2.22).
Women with anal sphincter injury at their first delivery are at almost a four fold risk for recurrent anal sphincter injury at the time of second delivery.
© 2012 Mosby, Inc. Published by Elsevier Inc. All rights reserved.