Screening occult anal sphincter injuries in primigravid women after vaginal delivery with transperineal use of vaginal probe: a prospective, randomized controlled trial.

Purpose: Here we aimed to evaluate the incidence of obstetric anal sphincter injuries in spontaneous primigravid deliveries with mediolateral episiotomy beyond 36 gestational weeks.

Methods: We performed a prospective, randomized controlled study including 201 primigravid women that delivered vaginally. Anal sphincter anatomy and integrity was evaluated before hospital discharge in all cases with transvaginal sonography (5-9 MHz) (Siemens Sonoline G50 and Voluson 730 Expert). The vaginal ultrasound probe is placed in the fourchette of the vaginal introitus to obtain the transverse section of the anal sphincter.

Results: In the cases with sphincter defect, mean gestational week and second stage of labor were prolonged significantly (p = 0.039 and p < 0.0001, respectively). The mean perineal body distance in cases with sphincter injury, as detected by sonography, 2.18 ± 0.33 cm, is compared to 2.31 ± 2.43 cm in cases without injury. There was a significant difference between the two groups (p = 0.0142). Shoulder dystocia was significantly higher in cases with sphincter injury, compared to cases without injury (p = 0.011). No clinical findings were reported in 11.5 % of cases (Sonography findings 1A∓, 1B∓) and 3.5 % of cases had clinical and sonographic findings (Sonography findings 2A∓, 2B∓). "Occult tears" were considered as those cases not detected clinically, but detected by sonography (11.5 % of all cases). Two months after examination, a moderate incontinence (Wexner continence scale) was found in 71.5 % of cases with overt sphincter tear, which was significantly different to the non-overt sphincter tear group. Multiple logistic regression analyses for sphincter injuries identified prolonged second stage of labor and shoulder dystocia as two independent risk factors.

Conclusion: Here, we found that only a portion of anal sphincter injuries can be detected after physical examination, with many of cases of "occult tears" escaping notice. These cases of occult anal sphincter injury are detectable by sonography with transperineal use of a vaginal probe. Based on these findings, we propose that this technique is convenient for obstetric, gynecologic and proctologic evaluation of sphincter anatomy.