Diagnosis of Obstetric Anal Sphincter Injuries (OASIs) Using Transperineal Ultrasound Scan (TPUS)

Overview

It is common for women to sustain perineal trauma following their first vaginal delivery. Sometimes these can extend to the anal sphincter, and these are referred to as Obstetric Anal Sphincter Injuries (OASIs). Occasionally OASIs may not be detected at delivery. If these tears are missed they would not be repaired and this may lead to incontinence of wind (flatus) or of faeces, both of which can have a significant impact on quality of life. The investigators would like to establish whether a 3D ultrasound scan probe placed outside the vagina can identify the anal sphincter defects and to investigate whether the use of TPUS immediately after primary repair of OASIs is an useful tool to minimise an inadequate repair. The investigators would also like to look at changes that occur to the pelvic floor muscles during labour and to identify injuries to the pelvic floor muscle (levator ani) by ultrasound. Such injury to pelvic floor muscle is associated with vaginal prolapse.

Following the first vaginal delivery 85% of women will sustain perineal trauma (1). Sometimes these can extend to the anal sphincter, and these are referred to as Obstetric Anal Sphincter Injuries (OASIs). Occasionally OASIs may not be detected at delivery. If these tears are missed they would not be repaired and this may lead to incontinence of wind (flatus) or of faeces, both of which can have a significant impact on quality of life. Endoanal ultrasound (where an ultrasound probe is inserted directly into the back passage) is the gold standard diagnostic tool to detect OASIs. It is however not available in most obstetric units. Transperineal ultrasound (where an ultrasound probe is placed on the perineum)(TPUS) in contrast is available in most obstetric units and therefore we wish to determine whether TPUS in addition to a routine clinical examination will increase the detection rate of OASIs. Anal incontinence can also occur if the anal sphincter are not repaired adequately. Therefore we want to investigate whether the use of TPUS immediately after primary repair of OASIs is an useful tool to minimise an inadequate repair. The other aim of the study is to look at changes that occur to the pelvic floor muscles during labour by ultrasound. It is known that certain muscle changes may lead to urinary incontinence and pelvic organ prolapse. However limited studies have evaluated the natural history of the pelvic floor muscles in labour. We therefore wish to perform a transperineal ultrasound each time the midwife or doctor caring for the woman in labour decides the woman in labour needs a vaginal examination. This will provide important information regarding changes that occur to the muscles of the pelvic floor during normal labour. References: 1)Byrd L,Hobbiss J,Tasker M. Is it possible to predict or prevent third degree tears? Colorectal Dis 2005;7:311-8.