Niche presence and changes of the uterine scar in the first year after caesarean section: A prospective longitudinal study

OBJECTIVE: To investigate the presence of uterine niches and changes in the uterine scar during the first year after caesarean section and determine the optimal time for scar evaluation. STUDY DESIGN: This prospective study included women who underwent their first caesarean section between May 2019 and November 2021. Transvaginal ultrasound was performed at 6 weeks, 10 weeks, 6 months, and 12 months post-surgery. Data on uterine niche presence and scar characteristics were systematically collected. RESULTS: Ninety-four women were included; 79 (84.0%) had repeated measurements. Attendance declined from n = 73 at 6 weeks to n = 53 at 12 months. At 6 weeks, a niche was observed in 62/73 (84.9%), with 62.9% of these classified as large.At 12 months, niche prevalence decreased to 41/52 (78.8%), with 53.7% classified as large. The uterine scar characteristics changed over time. Mixed model analyses revealed a significant decrease in RMT between 6 weeks and 6 months (-1.1 mm, 95% CI: -1.9 to -0.2, p = 0.02), followed by an increase between 6 and 12 months (+1.0 mm, 95% CI: 0.1 to 1.7, p = 0.04). Furthermore, significant differences in scar characteristics over time were found; length, depth and width decreased up to 6 months. CONCLUSION: Uterine scar measurements and niche prevalence decreased up to 6 months post-caesarean section, with a subsequent increase in RMT up to 12 months. It is therefore recommended to postpone evaluation of the uterine scar until at least 6 months after caesarean section, as most changes occur within this initial period.