Anal sphincter trauma during instrumental delivery.

OBJECTIVES: To determine the incidence of defecatory symptoms, pudendal nerve damage and mechanical trauma to the anal sphincters during vacuum and forceps delivery.

METHODS: Anal endosonography, manometry, pudendal nerve terminal motor latency (PNTML) measurements and perineometry were performed in 43 primiparae who had an instrumental delivery (17 vacuum and 26 forceps) and in 47 who had a normal vaginal delivery (controls).

RESULTS: Defecatory symptoms developed in 10 (38%) women following a forceps delivery compared with 2 (4%) in the control group (P = 0.0003), and 2 (12%) following a vacuum extraction (P = NS). Anal sphincter defects occurred in 21 (81%) forceps deliveries compared with 17 (36%) controls (P = 0.0005) and 4 (21%) vacuum extractions (P = NS). Anal pressures were lower in those who developed a sphincter defect (P < 0.00001). PNTML was not significantly altered by the mode of delivery.

CONCLUSIONS: Compared with vacuum extraction, forceps delivery is associated with significantly more damage to the anal sphincters and hence an increased incidence of defecatory symptoms.