Objective: The first aim of this study was to estimate the impact of anal sphincter laceration during the first delivery on the risk of recurrence in the second delivery. The second aim was to estimate the absolute risk of anal sphincter laceration in the second delivery according to the history of anal sphincter laceration and birth weight.
Methods: In this population-based cohort study, the study sample comprised all women included in the Norwegian Medical Birth Registry with 2 consecutive singleton vaginal deliveries during the period 1967-1998 (n = 486,463). The impact of prior anal sphincter laceration on recurrent anal sphincter laceration was estimated as crude and adjusted odds ratios (ORs).
Results: Anal sphincter laceration during first delivery increased the risk for a sphincter laceration in the next delivery, (adjusted OR 4.3, 95% confidence interval [CI] 3.8-4.8). Other risk factors were birth weight (adjusted OR 23.6, 95% CI 16.5-33.6, birth weight > 5,000 g versus birth weight < 3,000 grams), use of forceps (adjusted OR 5.1, 95% CI 4.3-6.0), use of vacuum (adjusted OR 1.4, 95% CI 1.1-1.7), and period of delivery (adjusted OR 4.3, 95% CI 3.7-5.0 for 1995-1998 versus 1967-1975). The absolute risks for anal sphincter laceration at second delivery for women with prior laceration were 1.3% (95% CI 0.4-3.2%) for birth weight less than 3,000 g and 23.3% (95% CI 11.8-38.6%) for birth weight more than 5,000 g.
Conclusion: Only 10% of women with anal sphincter laceration at second delivery had a history of prior laceration. Prior anal sphincter laceration is associated with increased risk of laceration in second delivery, in particular in women who carry children with high birth weight.
Level of evidence: II-2.