Long‐term complications of caesarean section. The niche in the scar: a prospective cohort study on niche prevalence and its relation to abnormal uterine bleeding

Objective To study the prevalence of niches in the caesarean scar in a random population, and the relationship with postmenstrual spotting and urinary incontinence. Design A prospective cohort study. Setting A teaching hospital in the Netherlands. Population Non‐pregnant women delivered by caesarean section. Methods Transvaginal ultrasound ( TVU ) and gel instillation sonohysterography ( GIS ) were performed 6–12 weeks after caesarean section. Women were followed by questionnaire and menstruation score chart at 6–12 weeks, 6 months, and 12 months after caesarean section. Main outcome measures Prevalence of a niche 6–12 weeks after caesarean section, using TVU and GIS . Secondary outcomes: relation to postmenstrual spotting and urinary incontinence 6 and 12 months after caesarean section; and niche characteristics, evaluated by TVU and GIS . Results Two hundred and sixty‐three women were included. Niche prevalence was 49.6% on evaluation with TVU and 64.5% with GIS . Women with a niche measured by GIS reported more postmenstrual spotting than women without a niche ( OR 5.48, 95% CI 1.14–26.48). Women with residual myometrium at the site of the uterine scar measuring <50% of the adjacent myometrial thickness had postmenstrual spotting more often than women with a residual myometrial thickness of >50% of the adjacent myometrial thickness ( OR 6.13, 95% CI 1.74–21.63). Urinary incontinence was not related to the presence of a niche. Conclusions A niche is present in 64.5% of women 6–12 weeks after caesarean section, when examined by GIS . Postmenstrual spotting is more prevalent in women with a niche and in women with a residual myometrial thickness of <50% of the adjacent myometrium.