2. United Lincolnshire Hospitals NHS Trust, UK.
3. Watford General Hospital NHS trust, UK.
Objective: Revisiting the risk factors associated with obstetric anal sphincter injuries (OASI) and their influence on the mode of delivery, whether spontaneous vaginal delivery (SVD) or operative vaginal delivery, and severity of tears.
Method: Retrospective audit, examining all cases of OASI over a six-month period. Power calculation confirmed adequacy of numbers for all analyses.Data were analysed by non-parametric tests.
Results: The total number of vaginal births was 1504, of which 40 had third degree tears (2.65%) with no fourth degree tears.
None of the women who had SVD (n=28) was given an episiotomy, but all those who had instrumental delivery were given a right medio-lateral episiotomy.
Maternal age did not influence the mode of delivery (p=0.8) or tear severity (p=0.8). The fetal weight (FW) did not influence the mode of delivery (p=0.56) nor did the BMI (p=0.1).
The parity and mode of delivery had no effect on the severity of the tears (p=0.13) nor did the mode of labour initiation (p=0.2) The first stage length did not affect the mode of delivery (p=0.5). The length of second stage did not affect the OASI extent (p=0.41).
Conclusions: 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 OASI degree.
None of the women with SVD had an episiotomy. Furthermore, there was no documentation of the maternal position during SVD or if ‘hands on’ technique was applied.
Keywords: Obstetric anal sphincter injuries, OASI, incontinence, pelvic floor