Mode of delivery following OASIS: A 5-year follow up study of subsequent deliveries after 3rd and 4th degree vaginal tears.

Rahim A1, Bhide A1, Mackdermott N2, Tailor V1, Patel M1, Digesu A1, Fernando R1, Khullar V1

Research Type


Abstract Category

Anorectal / Bowel Dysfunction

Abstract 24
Live Urogynaecology, Female & Functional Urology - Childbirth and its Consequences
Scientific Podium Session 3
Friday 15th October 2021
08:20 - 08:30
Live Room 1
Anal Incontinence Pelvic Floor Female Urgency, Fecal Retrospective Study
1. St. Mary’s Hospital, Imperial College NHS Trust, London, U.K., 2. Imperial College Medical School, London, U.K.

Asad Rahim



Hypothesis / aims of study
Obstetric anal sphincter injuries (OASIS) as a result of vaginal childbirth have the potential to lead to long-term issues with anal continence. There is limited data on management of subsequent delivery after OASIS. Further vaginal deliveries and recurrence of tears can further exacerbate symptoms. Providing women with the best, most accurate data on recurrence and symptomology forms one of the essential roles of the perineal/pelvic floor clinic (PFC). Such information can help women, as well as their clinicians, when balancing the risk of recurrence with the risks of caesarean delivery. The objectives of this study are to review the subsequent mode of delivery in women who have sustained an OASI in a previous pregnancy as well as assess the role of a specialized pelvic floor clinic in making decisions regarding choice of delivery.
Study design, materials and methods
We present retrospective, observational data of women who sustained a 3rd or 4th degree vaginal tear during their index delivery and subsequently underwent a further pregnancy. Data was collected from two maternity units located within a busy, multi-ethnic, urban region with a combined delivery rate of approximately 8500 deliveries per year. Women were included in the study if their index delivery occurred between 1st January 2014 and 31st December 2018, and their subsequent delivery occurred at anytime up until the 31st December 2020.    

Women who sustain an OASI in either of the two maternity units are typically invited to a specialized PFC during their subsequent pregnancy. A full history which includes assessment of faecal, urinary and perineal symptoms is elicited. AS recommended by RCOG guidelines (1), women are then offered an external perineal examination, anal manometry (AM) testing and endoanal ultrasound scan (EAUS). Anal manometry is performed using the Laborie® UDS GOBY 120 (Laborie Medical Technologies, version 12.0) using a 4Ch single channel pressure transducer. An initial anal resting pressure is taken followed by three squeeze pressures – the best of which is recorded for analysis. Endoanal ultrasound is performed in 2D and 3D using an Anorectal 3D 2052 probe attached to BK medical® Flex Focus 500. Review of all images and identification of sphincter defects is performed by one subspecialty-accredited Urogynaecologist. For this study we defined “symptomatic” women as having a history of persistent faecal urgency or incontinence with/without reduced manometry pressures and/or observed to have defects in one or both anal sphincters on EAUS.     

Data was compiled in Microsoft® Excel® format (v.2103, 2020) and converted to SPSS v.26 (IBM Corp. Armonk, NY) for analysis. Two-sided Fishers exact test was used to compare categorical variables with a cut off of p<0.05 being used to test for significance.
There were 642 women who sustained a 3rd (n= 616) or 4th (n=26) degree tear during our study period [Table 1]. Two-hundred and thirty-six women (37%) were known to have had a subsequent pregnancy following their initial OASI. The median inter-pregnancy interval was 23 months (4 – 66 months). The delivery outcomes of 11 women were unknown due to either incomplete records or the women rebooking their pregnancy at another maternity unit; 8 women (at the time of writing) are currently pregnant and therefore their delivery outcome remains pending.

Of the 217 women included [Table 2], 125 women achieved a spontaneous vaginal birth with a further 10 requiring an assisted vaginal delivery (62% vaginal delivery). Of the women who delivered vaginally, 6 had a recurrence of 3rd degree tear (4.4%). Sixty-seven women underwent an elective caesarean section due to previous OASI; 2 of these women had other indications for caesarean delivery (placenta praevia major and previous myomectomy). Fifteen women underwent an emergency caesarean section. 

One-hundred and five women attended a specialised pelvic floor clinic during the antenatal period of their subsequent pregnancy (between 17 and 38 weeks gestation). Most women (97%) underwent anal manometry and an endoanal ultrasound scan. The mean resting pressure was 50mmHg (range 25- 86mmHg) and the mean best squeeze pressure was 88mmHg (range 37 – 150mmHg). Forty-three women were defined as being symptomatic and of these, 21 (49%) chose to undergo an elective caesarean section.   

Amongst asymptomatic women attending pelvic floor clinic (n=62), 10 women opted to have an elective caesarean section for their upcoming delivery. A significant difference was observed in elective caesarean section rates when comparing this group to the group of women who were not reviewed in PFC during their subsequent pregnancy (16% vs 32%, p=0.03).
Interpretation of results
Most women who sustain an OASI continue to opt for and achieve a vaginal birth during a subsequent pregnancy. Recurrence of OASI remains uncommon and the role of a specialised PFC in predicting a recurrence remains unclear. What is clear however, is that the PFC does play an important role in helping women decide how they wish to deliver in a subsequent pregnancy. What this data has demonstrated is that by providing a dedicated antenatal service which assesses symptoms and uses objective tools such as manometry and EAUS, clinicians can adopt a more individualized approach to counselling women post-OASI than standard ante-natal counselling alone.
Concluding message
Third and fourth degree vaginal tears remains an important factor when women decide how to deliver in a subsequent pregnancy. In this 5-year follow up study, we have demonstrated that a specialised pelvic floor clinic plays a valuable role in the antenatal assessment of women who have sustained a prior OASI.
Figure 1 Table 1: Demographic and clinical data of all women who sustained an OASI between 1st January 2014 and 31st December 2018.
Figure 2 Table 2: Index and subsequent modes delivery in women who did and did not attend a specialised pelvic floor clinic during their subsequent pregnancy. CS= Caesarean section.
Funding NONE Clinical Trial No Subjects Human Ethics Committee IRAS ID 231312 Helsinki Yes Informed Consent Yes
05/07/2024 11:43:03