Objective: We prospectively evaluated the risk of recurrence of anal sphincter disruption ("third degree tear") at next vaginal delivery and whether this complication was predictable by antepartum anal functional assessment.
Study design: Among 20,111 consecutive vaginal deliveries, where midline episiotomy was not performed, 342 (1.7%) third degree tears occurred, significantly more often in primiparae (2.9%) than multiparae (0.8%; P<0.001), all of whom underwent postpartum anal manometry and endosonography. Similar testing was performed antepartum and postpartum in 56 of 342 women who delivered again during the study period.
Results: Eleven of 56 women were delivered by caesarean in next pregnancy. Third degree tears recurred in 2 (4.4%) of 45 women at next vaginal delivery. Both recurrent injuries occurred in asymptomatic women with normal antepartum manometry and following spontaneous deliveries and were satisfactorily repaired.
Conclusion: Although anal sphincter injury was increased five-fold at next delivery, compared with all multiparae, 95% of women delivering vaginally after previous third degree tear did not sustain further overt sphincter damage. Recurrence was not predictable using pre-delivery anal physiology testing.