A Search for Novel Risk Factors for Obstetric Anal Sphincter Injury

The objective of this study is to evaluate factors associated with obstetric anal sphincter injury and identify modifiable risks.

A retrospective case-control study was performed in women who gave birth at our institution between May 2008 and December 2012. Patients who had a third- or fourth-degree lacerations were compared with those who did not. Parity, stretch marks, age, body mass index, tobacco use, fetal weight, operative delivery, labor, and second stage duration were compared between groups. Multivariate direct logistic regression was conducted on all patients who had complete data to calculate the adjusted odds ratio.

We identified 299 patients with third- or fourth-degree lacerations and 8,459 patients without third- or fourth-degree lacerations during the time frame. Duration of second stage between 1 hour and 2 hours (P < 0.0001), duration of second stage greater than 2 hours (P < 0.0001), midline or unknown type episiotomy (P < 0.0001), mediolateral episiotomy (P < 0.0001), vacuum delivery (P < 0.0001), forceps delivery (P < 0.0001), fetal weight greater than 4,000 g (P < 0.0001), and antepartum stress urinary incontinence (P < 0.006) were associated with a significant increase in high-risk lacerations. This study did not find a statistically significant association between parity and these lacerations.

We, as others, found that episiotomy and operative delivery were modifiable risks of obstetrical care. Furthermore, even a short second stage of labor (1-2 hours) was associated with significant risk of injury.