Perineal Tears and OASI Recovery: Degrees, Follow-Up and Rehabilitation

A third or fourth degree perineal tear, together known as obstetric anal sphincter injury or OASI, extends into or through the anal sphincter complex, and it has an overall UK incidence of 2.9% with a range of 0 to 8%: 6.1% in women having a first baby against 1.7% in those who have given birth vaginally before, with vaginal births as the denominator throughout. NICE names injury to the anal sphincter as one of the specific triggers for considering a 3 month supervised programme of pelvic floor muscle training after birth¹².

I had two vaginal births and neither involved a sphincter injury, so this is not written from the inside. What I do remember is being handed a leaflet at a six week check that mentioned tears in one line, and I have thought since that the information arriving before the symptom would have been worth a great deal more than the information arriving after it. Read red flags and when to stop and get checked first: new faecal incontinence after childbirth is on that list and is urgent.

What the degrees describe

Depth, and therefore what has to heal.

• First degree: the skin of the perineum or vaginal wall only.
• Second degree: extending into the perineal muscle.
• Third degree: extending into the anal sphincter complex, subdivided by how much of the external and internal sphincter is involved.
• Fourth degree: extending through the sphincter complex into the lining of the anal canal.

Third and fourth together are what OASI means. They have a dedicated Royal College of Obstetricians and Gynaecologists guideline, Green-top Guideline No. 29, because their repair, their follow-up and their consequences differ from the first two¹. The International Continence Society maintains the standardised terminology used for the bowel and bladder symptoms that can follow³, which is why a clinic letter may describe something more precisely than a conversation did.

The incidence figures, with the denominator attached

This is the section where most online summaries slip, because the number changes completely depending on whether it is your first baby.

From the Royal College of Obstetricians and Gynaecologists¹:

• Overall UK incidence: 2.9%, range 0 to 8%.
• First vaginal birth: 6.1%.
• Women who have given birth vaginally before: 1.7%.
• Denominator throughout: vaginal births, not all births.
• The patient-facing version expresses the same thing as about 6 in 100 first births and fewer than 2 in 100 births for women who have given birth vaginally before.

A more than threefold difference between a first birth and a later one is the sort of thing that ought to be said out loud in an antenatal appointment and frequently is not. It is also the reason a figure quoted without saying which group it applies to is close to useless.

Why the reported rate rose, and why that is ambiguous

The same guideline records that the reported rate of OASI in England tripled from 1.8% to 5.9% between 2000 and 2012 in singleton, term, cephalic, vaginal first births¹.

A tripling in twelve years is striking, and the honest reading is that it is partly a reporting phenomenon. Better recognition and better recording both raise a reported rate without the underlying event becoming more common, and recognition matters clinically in a specific way: a tear that is identified at the time is a tear that can be repaired properly. So a rise in reported rates is compatible with an improvement in care as well as with a deterioration in outcomes.

This site therefore presents it as a reported rate and does not translate it into a claim about how often the injury actually occurs. That is the same discipline applied elsewhere here to any figure whose definition is doing heavy lifting.

What the follow-up is for

Assessing the repair, and asking the questions people do not volunteer.

Services differ enough between systems and hospitals that this site will not describe a single pathway, and pretending otherwise would be inventing detail. What a dedicated follow-up exists to do is check how the repair has healed, ask systematically about bowel control including flatus, about bladder symptoms, about pain and about sex, and decide what further investigation or treatment is needed.

The systematic asking is the valuable part. Bowel symptoms after birth are the least likely of all pelvic symptoms to be raised unprompted, and the appointment is short. Writing the difficult items on a list beforehand removes the need to find the right moment, because the right moment tends not to arrive. Faecal incontinence and anal sphincter training covers that symptom in full, including why it is a clinical question before it is a physiotherapy one.

What NICE actually recommends after a sphincter injury

One recommendation, with a weak verb and a specific trigger list.

NG210 recommendation 1.3.12 says to consider a 3 month programme of supervised pelvic floor muscle training during postnatal care for women who have experienced assisted vaginal birth using forceps or vacuum, an occipito-posterior vaginal birth, or injury to the anal sphincter². Two things follow from reading it carefully. The verb is consider, which is weaker than the offer used for stress and mixed urinary incontinence. And the trigger list is specific rather than a general category of women at risk.

The same guideline sets the structure any supervised programme should have: supervision by a physiotherapist or other healthcare professional with the appropriate expertise, at least one review to assess progress during the programme and one at the end, and continuation afterwards if it has been beneficial².

What the evidence supports, and where it does not

Here the site has to hold two things apart that are frequently merged.

For urinary symptoms around childbirth there is genuine evidence, and it favours starting in pregnancy rather than after birth. In the Cochrane review of pelvic floor muscle training in antenatal and postnatal women, continent women who began antenatal training were about 29% less likely to report urinary incontinence at 3 to 6 months postpartum than those receiving usual care, 179 per 1,000 against 251 per 1,000, a risk ratio of 0.71 with a 95% confidence interval of 0.54 to 0.95, from 5 trials and 673 women, graded high certainty⁴. Postnatal training as treatment did not show clear benefit in that review.

For faecal symptoms the picture is different and this site does not soften it. The same review found faecal incontinence outcomes consistently null and low certainty across every comparison⁴. So a page claiming that pelvic floor exercises fix bowel leakage after a tear is claiming something the largest relevant review does not support.

The World Health Organization’s postnatal recommendation runs alongside that. It does not recommend starting routine pelvic floor muscle training after childbirth for the prevention of postpartum urinary and faecal incontinence, while separately advising that women with involuntary loss of small volumes of urine after childbirth should be advised of the potential benefits of training as treatment for urinary incontinence⁵. Note again which symptom the treatment caveat attaches to.

What rehabilitation actually addresses

Load, emptying and the muscle, in that order of usefulness for most people.

Straining is the daily competing load, and after a repair it is also uncomfortable and worth avoiding for its own sake, so bowel management tends to come first: see bowel habit and defaecation technique and constipation and obstructed defaecation. Bladder symptoms are treated alongside, and about a third of women experience urinary incontinence in the first three months after childbirth in pooled data, with 33% having any incontinence, 12% weekly and 3% daily, and vaginal delivery at 31% against caesarean section at 15%⁶.

Muscle training, where it is used, is prescribed against an assessment rather than assumed. Return to load and impact is staged rather than permitted or forbidden: see returning to running and lifting. And scar and perineal discomfort, pain with sex, and guarding all belong in the assessment, because a floor that has become protective after an injury may be overactive rather than weak, which changes the direction of treatment entirely: see hypertonic pelvic floor and downtraining and pelvic pain and vaginismus.

Pelvic floor exercise programmes explained covers how a programme is built, and postnatal pelvic floor recovery covers the wider first year including what the six week check does and does not cover.

Getting seen, and what is published about access

Provision for this is better organised than for most pelvic symptoms in some places and absent in others.

NHS England has a perinatal pelvic health services programme, and the one defensible coverage fact this site holds is that 20 of 42 integrated care boards had a service in operation as at 16 May 2024, two months after the March 2024 universal coverage deadline⁷. No access or waiting-time data is published for those services at all. That absence is worth stating plainly rather than filling with a general community physiotherapy figure, which would describe a different queue.

Self-referral, where it exists for pelvic health, is frequently restricted to pregnancy and the first year after birth, which means this is one of the situations in which it is most likely to be available to you. Getting referred to pelvic health physiotherapy sets out the routes across five systems and pelvic health physiotherapy waiting times is written around what is and is not published.

The wider policy argument for that provision is on the record. The Independent Medicines and Medical Devices Safety Review recommended that pelvic floor education be encouraged in schools and certainly in antenatal classes, and that the NHS adopt the French model for universal postnatal pelvic floor rehabilitation, while noting in the same report that specialist pelvic floor physiotherapy cannot match the demand⁸. Pelvic floor physiotherapy sets out the treatment those recommendations are about.