Background
Obstetrical anal sphincter injuries (OASIS) involve third-degree and fourth-degree perineal tears after following vaginal delivery. The incidence of OASIS varies among different populations, and there are very few studies examining the incidence in Egypt. This study aimed to evaluate the incidence of OASIS, both overt and occult (ultrasound detected), among a cohort of primiparous women who delivered vaginally, and to assess the role of two-dimensional transperineal ultrasound (TPUS) in evaluating anal sphincter morphology.
Patients and methods
A prospective observational study included 124 primiparous women with singleton vaginal delivery during the first year after delivery. We excluded women with a history of chronic intestinal disease (Crohn's disease, ulcerative colitis), acute gastroenteritis within the week preceding consultation, those who underwent any surgical or diagnostic procedure involving the anal canal, and multiparous women. History was taken, examination was performed, and two-dimensional TPUS was performed. For the second objective, a control group of 43 primiparous women who delivered by cesarean section (CS) was recruited to compare the ultrasound findings with those of women who delivered vaginally with the same inclusion and exclusion criteria.
Results
Among the studied cohort of 121 women who delivered vaginally, no cases with overt OASIS were detected. Per rectal examination using pill-rolling motion to asses the thickness of the anal sphincter revealed 15 patients among the vaginal delivery group with poor thickness (representing 12.1%); on the other hand, in CS cases, all of them had normal thickness. Using TPUS for the evaluation of anal sphincter, we found three cases among those who delivered vaginally with disrupted mucosal star sign (2.4%) versus no cases in those who delivered by CS. The combined thickness of the internal and external anal sphincters was significantly thinner in the vaginal delivery group compared with the CS delivery group.
Conclusions
The study showed low incidence of both overt and occult OASIS among primiparous women who delivered vaginally; TPUS is a technique that is both simple and feasible to diagnose occult OASIS.