Transvaginal Ultrasonographic Measurement of Lower Uterine Segment in Term Pregnant Patients with Previous Cesarean Section

Background: With an aim to reduce the rates of repeat cesarean section in women with a previous scar, prediction of scar rupture or dehiscence is important. If we could predict the risk of rupture by measuring the scar thickness closer to term, we could pursue a trial of scar safely. Aims: To evaluate the use of ultrasound measured thickness of lower uterine segment as one of the predictors of scar rupture or dehiscence in labour and establish a cut off beyond which trial of labour can be attempted safely. Methodology: 187 randomly selected pregnant women with history of one previous cesarean section in the past who satisfied the inclusion criteria, attending the outpatient clinic over a period of six months, at a tertiary level teaching institution in southern India were selected and counseled to undergo a transvaginal measurement of the scar region. These women were then followed up until delivery and the outcome of trial of scar, successful vaginal delivery, rupture or dehiscence of uterus was analysed in relation to the scar thickness and various other contributing factors. Results: 187 women with history of previous cesarean section, attending the outpatient clinic were randomly chosen to undergo trans vaginal scan at term. 52 underwent elective cesarean section and 135 went through trial of scar. The median cut-off of the lower uterine segment in this study population of 135 was 2.4 mm. The sensitivity was 90.9%, specificity was 43.5%, positive predictive value was 12.5%, and negative predictive value was 98.3% at this cutoff for scar rupture or dehiscence. Conclusions: The lower uterine scar thickness could be a useful tool to predict scar rupture. This could aid in making decisions regarding induction of labour with oxytocin in women with previous cesarean section.