Background: Vaginal childbirth is a key risk factor for injury to the anal sphincter complex and for the later development of anal incontinence. Obstetric anal sphincter injuries (OASIS) may be overt or occult, and even when recognised and repaired, a proportion of women continue to experience bowel symptoms and deteriorated quality of life.[1-3] Clinical examination alone can underestimate the true burden of sphincter damage, and there is growing interest in imaging-based assessment of the anal sphincter in the immediate postpartum period.[2, 4] Transperineal ultrasound (TPUS) offers a simple, non-invasive method to visualise and measure anal sphincter morphology.[8-12]
Aim: To evaluate the immediate effect of vaginal delivery on internal anal sphincter (IAS) and external anal sphincter (EAS) thickness using two-dimensional (2D) transperineal ultrasound in primigravidae.
Materials and Methods: This prospective cohort study included 36 healthy primigravidae with term singleton cephalic pregnancies, planned for vaginal delivery, at a tertiary care teaching hospital in Karnataka, India. Women with previous anorectal surgery, known anal incontinence, gastrointestinal disease or third/fourth degree perineal tears were excluded. Standardised 2D TPUS examinations were performed within 24 hours prior to labour and repeated at 48 hours postpartum. IAS and EAS thickness were measured in millimetres at a predefined reference position by a single trained operator. Demographic and obstetric data (age, mode of delivery, neonatal birth weight) were recorded. Continuous variables were summarised as mean±standard deviation; categorical variables as frequency and percentage. Pre-post comparisons were made using paired t-tests, with p < 0.05 considered significant.
Results: Mean maternal age was 25.19±3.53 years; half of the women (50.0%) were 26-30 years and 38.9% were 21-25 years. Normal vaginal delivery occurred in 31 women (86.1%), and 5 (13.9%) had vacuum-assisted delivery. The mean neonatal birth weight was 2.94±0.24 kg; 91.7% of babies weighed 2.5-3.5 kg. Before labour, mean EAS thickness was 2.20±0.33 mm (range 1.536-2.662 mm) and mean IAS thickness was 2.57±0.10 mm (range 2.422-2.828 mm). At 48 hours postpartum, mean EAS thickness decreased to 1.91±0.24 mm (range 1.522-2.233 mm), and mean IAS thickness decreased to 1.93±0.17 mm (range 1.677-2.325 mm). The mean reduction in IAS thickness was 0.64±0.18 mm (t = 20.784; p < 0.001) and in EAS thickness 0.29±0.20 mm (t = 8.939; p < 0.001).
Conclusion: Vaginal delivery in primigravidae is associated with a significant immediate reduction in both internal and external anal sphincter thickness as assessed by 2D TPUS, with a more pronounced effect on the IAS. Incorporating TPUS into early postpartum assessment may help detect subclinical sphincter changes and identify women at risk of later anal incontinence.
International Journal of Clinical Obstetrics and Gynaecology
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