Overall incidence of obstetric anal sphincter injury 4.9 percent

(HealthDay)—The incidence of obstetric anal sphincter injury is 4.9 percent, and risk factors include vacuum-assisted vaginal delivery and prolonged duration of second stage of labor, according to a study published online Jan. 9 in Obstetrics & Gynecology.

Olga Ramm, M.D., from the Kaiser Permanente Oakland Medical Center in California, and colleagues conducted a retrospective cohort study including 22,741 singleton, term, cephalic, vaginal deliveries to examine the incidence of obstetric anal sphincter injuries, defined as third- or fourth-degree perineal lacerations.

The researchers found that the overall incidence rate of obstetric anal sphincter injuries was 4.9 percent (3.6 and 24.0 percent among women who delivered spontaneously versus those who had a vacuum-assisted vaginal delivery, respectively; P < 0.001). The odds of obstetric anal sphincter injury were increased for women with vacuum-assisted vaginal delivery (adjusted odds ratio, 4.23) and for those whose second stage of labor lasted at least 180 minutes versus less than 60 minutes (adjusted odds ratio, 3.20). In addition to vacuum-assisted delivery and a labor lasting longer than two hours, bivariate and multivariate analyses also showed a higher incidence of obstetric anal sphincter injury in Asian women and those giving birth for the first time, as well as in women who had a vaginal birth after cesarean delivery or an episiotomy.

"Vacuum-assisted vaginal delivery conferred the highest odds of obstetric anal sphincter injury followed by prolonged duration of the second stage of labor, particularly among certain subpopulations," the authors write.

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