Risk factors for anal sphincter injury during vaginal delivery

Abstract EN

Objective: To determine the risk factors that may lead to occult injury of the anal sphincter or pudendal nerve during normal or assisted vaginal delivery.

Study design: We compared the results of bowel function questionnaire, quantitative EMG changes, and anal endosonography in 70 pregnant women , before and 6-8 weeks after delivery.

They were classified into 3 groups, Group I, 30 nullipara delivered vaginally (normal and assisted) ; Group II, 30 multipara delivered vaginally (normal and assisted) and Group III, (control grroup) delivered by elective cesarean sections.

Postpartum pudendal nerve terminal motor latency was measured in all women.

Results: In Group I, prolonged gestational age, duration of labor > 12 hours and oxytocin augmentation were associated with altered fecal continence, OR = 2.3, 95% CI = (1.3 - 4.1); 2.8, (1.6 - 4.7) and 2.04, (1.52 - 6.25) respectively.

But these factors were not associated with altered fecal continence in Group II, OR = 1.8, 95% CI = (0.91 - 1.66) ; 0.8, (0.4-1.1) and 1.4, (0.3-5), respectively.

Odds ratio of instrumental delivery in Group I, who complained of fecal incontinence was, OR = 16.6, 95% CI = (12.3-30), while in Group II, it was, OR = 9.94, 95% CI = (7.2-12.4), p < 0.001.

Odds ratio of perineal tear in symptomatic nulliparous women was, OR = 11.3, 95% CI = (4.6-31.3), p < 0.001, while in symptomatic multipara it was, OR = 9.2, 95% CI = (7.1-12.2), p < 0.001.

Postpartum QEMG changes of the external anal sphincter was observed in 5 (17%) in Group I, 3 (60%) of them had instrumental deliveries, OR = 7.3, 95% CI = (4.0 - 13.2), p < 0.001 and 2 (40%) of them had prolonged second stage of labor, OR = 2.55, 95% CI = (1.03 - 2.30), p < 0.001.

In Group II, prolonged second stage was not associated with postpartum QEMG changes of the external anal sphincter.

Perineal tears were found in 3 (60%) women in Group I, who had EMG changes, OR = 6.2, CI = (5 - 17), p < 0.001.

Again, in Group II, 6 (20%) women, had postpartum QEMG changes recorded from their external anal sphincter, 2 (33%) of them had instrumental delivery, OR = 6.6, 95% CI = (5 - 17), p < 0.001and 3 (50%) of them had perineal tear, OR = 5.5, 95% CI = (5-15), p < 0.001.

There was a significant increase in the mean PNTML in the multiparous group as compared to the nulliparous or control groups p < 0.001.

Postpartum anal endosonogaphic study in the control group showed that there was no defect in either external or internal anal sphinicters.

But in Group I, 8 (26%) women had anal endosonographic defects and in Group II, 5 (16%) women had anal endosonographic defects Conclusion: Instrumental delivery and prolonged second stage of labor are the greatest risk factors for the development of anal sphincter injury and dysfunction after vaginal delivery.

Electromyography (EMG), pudendal nerve terminal motor latency and anal endosonography are conclusive for the evaluation of subclinical patients with fecal incontinence.