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.