Anal sphincter disruption at vaginal delivery: is recurrence predictable?

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.

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.

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.

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.