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Obstetric Anal Sphincter Injury (OASI) in childbirth

Obstetric Anal Sphincter Injury (OASI) is an injury suffered by women during childbirth.

OASI involves damage to the perineal and anal sphincter muscles. The more severe the injury the further into the anal sphincter the tear extends.

What are third and fourth degree tears?

OASI injuries are categorised as third and fourth degree tears. While a second degree tear will extend into the perineal muscles only, a third degree tear will also involve a partial tear of the anal sphincter and a fourth degree tear will involve a complete tear of the anal sphincter.

If third and fourth degree tears are recognised at the time of the birth and repaired appropriately then women can have a good outcome. This is known as a primary repair. Even if it is missed or mis-managed at the birth some women will still have a good outcome following secondary repair. However, for some women the impact of OASI will be permanent and they will suffer ongoing pain and urinary and/or faecal incontinence. 45% of these women will also suffer postnatal depression as a result of their injuries.

How common are third and fourth degree tears?

According to the RCOG (Royal College of Obstetricians and Gynaecologists) 2014 Blog entitled Perineal tearing is a national issue we must address 90% of women tear during childbirth. The Blog considered some of the findings of the BJOG study which had been published the previous year, “Third- and fourth-degree perineal tears among primiparous women in England between 2000 and 2012: time trends and risk factors.” This study considered third and fourth degree tears in first time mothers and found that between 2000 and 2011 there had been a three-fold increase in the rate of reported third and fourth degree perineal tears in all NHS hospitals in England, with the rate rising from 1.8% in 2000 to 5.9% in 2011. It was stated that “the College, along with the RCM, are currently planning joint work to improve the awareness of third and fourth degree tears’ among health professionals involved in maternity care and develop tools to improve the prevention and management of severe perineal tearing.”

Given these findings and the intended push to improve awareness among health professionals, prevention and management of severe perineal tears, you may expect the position for mothers to be significantly improved. However, in the NHS England “Better Birth Four Years On: A review of progress” report published by NHS England in March 2020 it found that between 2016-2017 the rate of third and fourth degree tears in first time mothers who had spontaneous vaginal births was 5.1% and first time mothers who had instrumental births the rate was 7.1%. These statistics suggest that around 6% of first time mothers continue to suffer severe perineal tears during childbirth.

Evidence suggests that incidences of third and fourth degree tears may be higher in first time mothers, in births where the baby is in the occiput posterior (OP) position, in births where the baby is of a high birth weight and during instrumental delivery.

Where can I get help following an anal sphincter injury?

There is clearly significantly more required to be done to improve awareness of the issue and potential risk factors in health professionals who are involved in maternity care, to reduce the incidences of OASI and ensure better management of such injuries and support for women when they do occur.

Organisations such as The Masic Foundation raise awareness of the issues and help women who have suffered OASI.

If you, or someone you know, has suffered a similar injury and would like further advice in relation to pursuing a legal claim, then we would be happy to speak with you.


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