Sphincter Tear Rate Falling in Vaginal Births


TUCSON, ARIZ. — The rate of anal sphincter laceration during vaginal delivery has declined sharply in recent years, paralleling modifications in obstetric practice, a University of Southern California study revealed.

Anal sphincter laceration occurred in 11.2% of vaginal deliveries at the colossal Los Angeles County/USC Medical Center in 1996, compared with 7.9% in 2004, with about a 6% reduction in risk every year after 1996, reported Dr. Steven Minaglia at the annual meeting of the Society of Gynecologic Surgeons.

“Changes in obstetric practice, such as the increase in cesarean section and the decrease in operative delivery and episiotomy, may have contributed to the dramatic reduction in sphincter laceration,” Dr. Minaglia said.

During the time period studied, episiotomies declined from 9% to 8% of vaginal deliveries, vacuum deliveries from 5.1% to 2.9%, and forceps deliveries from 1.7% to 0%. “Of note, the C-section rate went from 18.2% to 32.3%,” he said.

The retrospective study assessed characteristics in 1,703 patients who had an anal sphincter laceration and 14,964 who did not have such an injury, for a total of 16,667 singleton vaginal deliveries at greater than 20 weeks of gestation. Younger age, lower parity, and higher birth weight all were associated with a higher likelihood of an anal sphincter laceration.

Other important risk factors independently associated with a laceration included vacuum delivery (odds ratio 3.19), forceps delivery (OR 2.79), episiotomy (OR 1.36), shoulder dystocia (OR 2.03), and gestational age (OR 1.03, about a 4% increased risk for each week of gestation).

Dr. Minaglia, of the division of female pelvic medicine and reconstructive surgery, encouraged a further minimization of modifiable risk factors such as episiotomy and operative delivery to minimize long-term harm associated with sphincter laceration.

A second study presented at the meeting found similar risk factors at the University of New Mexico Hospital in Albuquerque, where episiotomy and operative vaginal delivery rates are 5%–25% lower than national rates.

The case-control study matched 350 women who sustained a third- or fourth-degree anal sphincter laceration to 716 women matched by gestational age and chronologic time of delivery who did not have a laceration.

The risk of an anal sphincter laceration increased with vacuum extraction (OR 5.96), forceps extraction (OR 11.05), and episiotomy (OR 2.34,); as well as maternal age (OR 1.09 per year); and infant weight (OR 1.09 per 100 g).

As in the USC study, multiparity was protective, reported Dr. Alana Williams and associates in a poster presentation.

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