A revisit to the risk factors and delivery techniques associated with obstetric anal sphincter injuries (OASI)

Bachkangi P1, Saleh M2, Harris R2, Salman M2

Research Type


Abstract Category

Anorectal / Bowel Dysfunction

Abstract 87
E-Poster 1
Scientific Open Discussion ePoster Session 7
Wednesday 4th September 2019
12:40 - 12:45 (ePoster Station 3)
Exhibition Hall
Anal Incontinence Pelvic Floor Urgency, Fecal Prevention
1.University Hospitals of Leicester NHS Trust, 2.United Lincolnshire Hospitals NHS Trust

Panayoti Bachkangi




Hypothesis / aims of study
The overall incidence of obstetric anal sphincter injuries (OASIS) in the UK is 2.9%. 6.1% of primiparae labourers and 1.7% of multiparae women experience this complication (1). In the UK the incident of OASI has tripled from 1.8% to 5.9% from 2000 to 2012.
OASIS if not treated appropriately it can lead to faecal incontinence, perineal pain, sexual and urinary problems.

To revisit the risk factors associated with OASI and their influence on the type of delivery, whether spontaneous vaginal delivery (SVD) or instrumental delivery (ID).
Study design, materials and methods
Descriptive retrospective cross-sectional study set in a busy UK district general hospital.

Immediate post-partum women having a third or fourth degree perineal tear.

A retrospective audit, conducted in our department, examining all cases of OASI over the six-month period from January the 1st to June the 30th of 2018. The cases were identified from the birth register and the information obtained from the medical notes and Medway Maternity System. 

The data were analysed by non-parametric tests, and further post-hoc power/size calculations confirmed adequacy of numbers for all analyses.
1504 women had vaginal birth, of which 40 (2.65%) had third degree tears: 18 women had 3a, 19 had 3b and 3 had 3c tears. There were no fourth degree tears. 

28 women had spontaneous vaginal delivery (SVD), 6 had forceps and 6 ventouse deliveries. 26 women were primeparous, 10 had one previous vaginal delivery and 4 had two or more. Parity did not influence the mode of delivery (ID or SVD) (Chi-square, p= 0.13).

None of the women who had SVD was given an episiotomy, but all 12 women who had ID were given a right medio-lateral episiotomy.

The mean age was 30 years and it did not influence the mode of delivery (ID vs SVD; Mann Whitney test, p= 0.8) or severity of tear ((3a vs 3b vs 3c; Kruskal-Wallis test, p= 0.8). 

The fetal weight did not influence the mode of delivery (ID vs SVD, p=0.56). The mean FW were 3444gr, 3728, and 3423, in the groups of SVD, forceps and ventouse deliveries respectively and did no show significant difference among these groups (Kruskal-Wallis test, p= 0.17).

The mean BMI was 25 with that of 21 women being from 20 to 25. The BMI did not affect the mode of delivery (ID vs SVD; p= 0.1) or the degree of tear (3a vs 3b vs 3c; Kruskal-Wallis test, p= 0.2).

24 women had a spontaneous labour and 16 had induction of labour (IOL), but this did not affect the degree of tears (Chi-square, p= 0.2). 4 women had epidural analgesia, which did not influence the mode of delivery (Fisher's exact test, p=0.5).

The length of the first stage (in minutes) did not affect the mode of delivery (p= 0.5) even though it was much longer in women who had ID.

Women who had a SVD had a significant shorter second stage (p= 0.0008) than those having ID. The second stage length did not affect the tear severity (p= 0.41) despite the obvious worsening with prolonged labour (Mean± SD: 3a: 41.22±42.46; 3b:76.89±42.46; 3c: 98.33±42.46)

A mild negative correlation between FW and BMI (Spearman’s; p= 0.05 – r= -0.3)
Interpretation of results
Most OASI were in primiparous and in SVD. Maternal age, BMI, FW and first stage length did not affect the mode of delivery. 

Prolonged second stage increased the risks of instrumental delivery and of worsening degree of OASI. However, neither the type of delivery nor the FW did influence the severity of OASI. 

None of the women with SVD had an episiotomy, something that raises the question if a prophylactic episiotomy could have reduced the incidence of OASI. Furthermore, there was no documentation of the maternal position during SVD or if ‘hands on’ technique was applied.
Concluding message
The vast majority of OASI happen with spontaneous vaginal deliveries in low-risk women. These findings raise the question if the application of 'hands on' technique could have a preventive role. 

An antenatal assessment of pregnant women may identify those at risk of OASI and, therefore, a primary prevention can be offered and OASI can be prevented.
  1. Royal College of Obstetricians and Gynaecologists: Third- and Fourth-degree Perineal Tears, Management (Green-top Guideline No. 29)
Funding Not applicable Clinical Trial No Subjects Human Ethics not Req'd It is a retrospective audit Helsinki not Req'd It is a retrospective audit Informed Consent No