Detection of Occult Anal Sphincter Injuries in Primipara by 2D Transperineal Ultrasound and its Clinical Association: A Cohort Study

Introduction: Endoanal Ultrasound (EAUS), the gold standard for the detection of occult Obstetric Anal Sphincter Injuries (OASI) has limited clinical application due to its intrusiveness and need for specialised equipment and personnel. A 2D Transperineal Ultrasound (TPU) is simple, non invasive and shows a high degree of agreement with EAUS. Few studies have evaluated the use of 2D TPU in determining the incidence and clinical outcomes of occult OASI in primigravida.

Aim: To study the incidence, risk factors, and clinical outcome of occult obstetric anal sphincter injury using 2D TPU in primigravida.

Materials and Methods: The present cohort study was conducted in the Department of Obstetrics and Gynaecology in collaboration with the Department of Radiology at Guru Teg Bahadur Hospital, Delhi, India, from November 2018 to April 2020. A total of 200 low risk primigravida ≥36 weeks period of gestation underwent baseline TPU of the anal sphincter complex antenatally and on day 2 postpartum. On the basis of difference between pre and postdelivery measurements, they were divided into group I (n=91): women with occult OASI (diagnosed as thinning of the internal and External Anal Sphincter (EAS), interruption in the anal sphincter, alteration in mucosa and half-moon sign) and group II (n=109): no OASI. Group I was followed at two and six weeks postpartum with TPU and clinical tests were applied at 6 weeks to assess clinical outcomes of sphincter injury. Data was analysed using Chi-square test/Fisher’s-exact test for qualitative parameters, Analysis of Variance (ANOVA) for comparison of predelivery and postpartum measurements; and multiple logistic regression for determining sphincter injury determinants.

Results: Incidence of occult OASI was 91/200 (45.5%). Significant risk factors for OASI were lower baseline thickness of anal sphincter, position of baby (p=0.028), longer duration of second stage of labour (p<0.001), greater length and angle of episiotomy (p<0.001) and greater baby weight (p=0.042). Group I had significantly lower pelvic floor muscle strength testing score (p<0.001), Digital Rectal Examination Scoring System (DRESS) resting (p=0.013) and squeeze scores (p=0.008), weaker muscle contraction (p<0.001), reduced anal sphincter tone, and was more clinically symptomatic at six weeks postpartum.

Conclusion: The technique of 2D TPU is simple and feasible to detect OASI. Women, who sustain OASI, can be followed up in perineal clinic more meticulously, using TPU for pelvic floor rehabilitation.