Abstract: We included one trial that randomised 752 primiparous women with clinically detectable second-degree perineal tears to either further assessment with EAUS prior to perineal repair or standard care. We assessed this trial as being at a low risk of bias. The trial reported women's anal incontinence at three and 12 months as well as their pain scores and quality of life assessment. The trial authors reported outcomes at three months for 719 women (364 in the experimental group, 355 in the control group, 4% loss to follow-up), and an outcome at 12 months for 684 women (342 in the experimental group, 342 in the control group, 9% loss to follow-up). Primary outcome Compared with clinical examination (routine care), the use of EAUS prior to perineal repair was associated with a reduction in the rate of severe anal incontinence (defined as involuntary loss of faeces or flatus that constitutes social and/or hygiene problems, or as defined by authors), at greater than six months postpartum (risk ratio (RR) 0.48, 95% confidence interval (CI) 0.24 to 0.97, 684 women at the 12-month time point). Secondary outcomes Severe anal incontinence at less than six months was reduced with the use of EAUS prior to repair when compared with clinical examination (routine care) (RR 0.38, 95% CI 0.20 to 0.72, 719 women). However, increased perineal pain at three months was associated with the use of EAUS prior to perineal repair when compared with routine care (RR 5.86, 95% CI 1.74 to 19.72, 684 women). There was no clear difference in the number of women who reported any anal incontinence at either less than six months or equal to or greater than six months (outcomes not prespecified in our published protocol). Similarly, there was no clear difference between groups in terms of faecal incontinence, flatal incontinence, faecal urgency, or maternal quality of life. The study did not report any data on the need for secondary repair of external anal sphincter, dyspareunia, women's satisfaction with care or the planned or actual mode of birth in any subsequent pregnancy. We were unable to assess the detection rates of OASIS with EAUS from the included study because women with clinically-detected OASIS were excluded from randomisation. There is some evidence to suggest that EAUS prior to perineal repair is associated with reduced risk of severe anal incontinence but an increase in the incidence of perineal pain at three months postpartum. However, these results are based on one small study involving 752 women. The study took place in a large teaching hospital with an average to busy labour ward. The trial participants were similar to those found in most large obstetric units in developed countries, thus increasing applicability of the evidence, but were restricted to primiparous women. More research is needed to further evaluate the effectiveness of EAUS in the detection of OASIS following vaginal birth and in reducing the risk of anal sphincter complications related to OASIS. More high-quality RCTs are needed to fully evaluate the intervention before the routine use of EAUS on the labour ward could be supported. It would be particularly useful if future trials could assess detection rates of OASIS with EAUS versus clinical examination alone as this is the basis of the theory for improved outcomes with this intervention. Cost and the training required to implement EAUS should be considered, along with maternal quality of life and individual symptoms experienced by postnatal women . It would also be useful to follow up women after their subsequent vaginal births to determine if subsequent mode of delivery affects long-term outcomes. Future studies in multiparous women may also be useful.

Plain-language summary: We found one randomised controlled trial that met our inclusion criteria. This trial included 752 women who, following vaginal birth, had a tear to the skin between the vagina and anus that did not include the anal muscles on clinical examination. The women were allocated to receive either routine care (clinical examination) or anal ultrasound prior to their tear being sutured (stitched). We found that women who had anal ultrasound before undergoing perineal repair were about half as likely to suffer from severe anal symptoms. This difference was clear at less than six months and greater than or equal to six months after giving birth. Women were, however, more likely to have significant perineal pain at three months after birth if they underwent ultrasound examination. Solid stool incontinence and involuntary loss of gas (flatulence) were not clearly different between the two groups of women. There was also no difference in terms of maternal quality of life. The study did not report on the need for secondary repair of external anal sphincter, the number of women who reported pain during sexual intercourse, women's satisfaction with care or details relating to mode of birth in any subsequent pregnancy. It was not possible to look at how effective anal ultrasound examination was at detecting anal sphincter injuries because women with clinically-detected obstetric-related anal sphincter injury were excluded from the study. We assessed the included trial as being at low risk of bias as it was a well designed trial, but it involved a small number of women. More trials are needed in this area to further evaluate this intervention and inform future practice. We did not find any studies that used ultrasound after the tear had been sutured. It would be helpful if future studies could evaluate how effective ultrasound is at detecting obstetric anal sphincter injury. The cost of the intervention and any training needs should be considered, along with maternal quality of life and individual symptoms experienced by postnatal women. It would also be useful to examine how women give birth with subsequent pregnancies and longer-term outcomes.