3RD DEGREE OBSTETRIC ANAL-SPHINCTER TEARS - RISK-FACTORS AND OUTCOME OF PRIMARY REPAIR

Objectives-To determine (i) risk factors in the development of third d egree obstetric tears and (ii) the success of primary sphincter repair . Design-(i) Retrospective analysis of obstetric variables in 50 women who had sustained a third degree tear, compared with the remaining 85 53 vaginal deliveries during the same period. (ii) Women who had susta ined a third degree tear and had primary sphincter repair and control subjects were interviewed and investigated with anal endosonography, a nal manometry, and pudendal nerve terminal motor latency measurements. Setting-Antenatal clinic in teaching hospital in inner London. Subjec ts-(i) All women (n = 6603) who delivered vaginally over a 31 month pe riod. (ii) 34 women who sustained a third degree tear and 88 matched c ontrols. Main outcome measures-Obstetric risk factors, defaecatory sym ptoms, sonographic sphincter defects, and pudendal nerve damage. Resul ts-(i) Factors significantly associated with development of a third de gree tear were: forceps delivery (50% v 7% in controls; P = 0.00001), primiparous delivery (85% v 43%; P = 0.00001), birth weight > 4 kg (P = 0.00002), and occipitoposterior position at delivery (P = 0.003). No third degree tear occurred during 351 vacuum extractions. Eleven of 2 5 (44%) women who were delivered without instruments and had a third d egree tear did so despite a posterolateral episiotomy. (ii) Anal incon tinence or faecal urgency was present in 16 women with tears and 11 co ntrols (47% v 13%; P = 0.00001). Sonographic sphincter defects were id entified in 29 with tears and 29 controls (85% v 33%; P = 0.00001). Ev ery symptomatic patient had persistent combined internal and external sphincter defects, and these were associated with significantly lower anal pressures. Pudendal nerve terminal motor latency measurements wer e not significantly different. Conclusions-Vacuum extraction is associ ated with fewer third degree tears than forceps delivery. An episiotom y does not always prevent a third degree tear. Primary repair is inade quate in most women who sustain third degree tears, most having residu al sphincter defects and about half experiencing anal incontinence, wh ich is caused by persistent mechanical sphincter disruption rather tha n pudendal nerve damage. Attention should be directed towards preventi ve obstetric practice and surgical techniques of repair.