Strengths and limitations
The strengths of this study are that validated methods of ultrasound assessment were used to evaluate the anal sphincter complex. A power calculation was undertaken to establish the incidence of OASIs and an adequate sample size was achieved. Our study is the first to correlate clinical findings with TPUS in women undergoing their first vaginal delivery immediately postpartum. All TPUS scans were reviewed blindly without prior knowledge of clinical findings, thereby reducing the risk of detection bias.
The limitations of our study are that it was a single centre study, and most of the women were nulliparous, this decreases the prospect of generalisability. All the scans were performed by a single operator, which can potentially introduce significant bias; however, this factor also allowed for standardisation of the scans. It is acknowledged that the number of women who sustained OASIs is relatively small.