Introduction Third degree tears complicate 1.7 to 18% of vaginal births. Although many women are asymptomatic by twelve month follow-up, there is concern regarding management of future pregnancies, particularly mode of birth. It has been suggested that lesions identified by endo-anal ultrasound (EAUS) and the presence of symptoms can be used to inform decision making about mode of birth in subsequent pregnancies. We aimed to ascertain the incidence of 3A tears, the proportion with symptoms and/or observable sphincter defects using EAUS and mode of birth in subsequent pregnancies.

Method A Retrospective three year analysis was undertaken on all third/fourth degree tears between 2009 and 2011.

Results 361 cases (2.2% of vaginal births) of third/fourth degree were identified, 182 were 3A tears. Information was available for 96/182 women at twelve week postnatal follow-up, overall 78/96 (81%) had EAUS and 68/96 (71%) were asymptomatic.

Of the women who had EAUS, 56/68 (82%) were asymptomatic and 22/28 (79%) were symptomatic, 49/56 (88%) and 19/22 (86%) respectively had no observable defect.

17/96 women with 3A tears went on to have subsequent pregnancies. 15/17 (88%) delivered vaginally. All women with EAUS identified sphincter defects delivered vaginally. 66% of symptomatic women delivered vaginally.

Conclusion Our third degree tear rate is within expected limits. Flatal/faecal incontinence is a poor indicator for the presence of a significant sphincter defect on EAUS. Neither symptoms nor detection of sphincter defect appears to influence subsequent management or mode of birth, therefore the use of this invasive test is of questionable clinical benefit.