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.