Fetal head circumference and length of second stage of labor are risk factors for levator ani muscle injury, diagnosed by 3-dimensional transperineal ultrasound in primiparous women.

Abstract

We evaluated rate of levator ani muscle (LAM) avulsion among primiparae using 3-dimensional transperineal ultrasound to identify possible risk factors for such trauma. We conducted a prospective observational study. Three-dimensional transperineal ultrasound was performed on all subjects. Primiparae were evaluated 24-72 hours after vaginal delivery. In all, 32 nulliparous gravidae (35-41 weeks) and 15 elective cesarean delivery primiparae were evaluated as methodological controls. We compared newborn head circumference (HC), birthweight, second stage duration, maternal age, baby sex, episiotomy, and instrumental delivery. LAM trauma was observed in 39 of 210 (18.8%) patients and no controls. Odds ratio for LAM trauma when newborn HC >or= 35.5 cm was 3.343 (95% confidence interval, 1.33-8.42); when second stage duration >or= 110 minutes, odds ratio was 2.27 (95% confidence interval, 1.07-4.81). Logistic regression showed that HC >or= 35.5 and second stage duration >or= 110 minutes increased odds of LAM trauma by a factor of 5.32. Large HC and prolonged second stage duration are risk factors in LAM trauma. Elective cesarean delivery may prevent LAM trauma.