What is an Obstetric Anal Sphincter Injury (OASIS)?
When women have a baby vaginally, 85-90% will have some degree of trauma to the vagina and/or the perineum, the area between the anus and the opening to the vagina. Occasionally, this can include the anal sphincter, also known as an OASIS.

At the Pelvic Floor Unit, Dr Karantanis works closely with the Colorectal team at St George Hospital, and has established a specialised clinic for women with Obstetric Anal Sphincter Injury (OASIS). The clinic cares for women who have had extended vaginal tears during childbirth which may affect their bowel function.

A visit will be arranged at 6 weeks and 6 months after delivery to discuss any issues you may be having and future pregnancies. The first visit will often be with a specialised physiotherapist as it is important to continue doing your pelvic floor exercises. At 6 months you may have special tests performed, called anorectal physiology studies, and an endoanal ultrasound, to further investigate the function of your sphincter. This will give an indication of how well your sphincter and nerves are working and may help guide your next delivery.

What are the long-term implications of an OASIS?
If the injury is identified and repaired correctly, most women will have no long-term consequences, however up to 9% may suffer from faecal incontinence (undesired leakage of stool) and up to 24% some type of anal incontinence (uncontrolled leakage of wind, liquid or solid stool). Up to 21% of women will have faecal urgency (not being able to defer going to the toilet to open your bowels for longer than 15minutes). However, up to 11% of women who have a baby without an OASIS, including those that have a caesarean section, will also suffer from anal incontinence. Fortunately most of the symptoms will resolve by 12 months with physiotherapy and dietary modifications. Unfortunately OASIS is the major contributing factor to anal incontinence in postmenopausal women. If your symptoms persist, other treatments such as surgery are available, but we recommend you wait until your family is complete.

What about future pregnancies?
You will need to discuss mode of delivery at your next pregnancy at your follow up visit. As there is currently no clear evidence to suggest one mode of delivery over another once you have had an OASIS, your doctor will discuss the options of a vaginal delivery versus a caesarean section. If you are asymptomatic, do not have any faecal incontinence, and have a normal ultrasound and physiology studies then you may elect for a vaginal delivery, however you are at a 7.2% risk of suffering a severe tear again. If you had faecal incontinence immediately after your delivery that resolved, you have a 1 in 6 chance of developing permanent symptoms following a subsequent vaginal delivery. If you have some symptoms, or are asymptomatic but have abnormal tests, your treating doctor may discuss with you having a caesarean section for your future pregnancies.


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