title: Prevalence, potential risk factors for development and symptoms related to the presence of uterine niches following Cesarean section: systematic review.
abstract: OBJECTIVE
  To review systematically the medical literature reporting on the prevalence of a niche at the site of a Cesarean section (CS) scar using various diagnostic methods, on potential risk factors for the development of a niche and on niche-related gynecological symptoms in non-pregnant women.
  
  
  METHODS
  The PubMed and EMBASE databases were searched. All types of clinical study reporting on the prevalence, risk factors and/or symptoms of a niche in non-pregnant women with a history of CS were included, apart from case reports and case series.
  
  
  RESULTS
  Twenty-one papers were selected for inclusion in the review. A wide range in the prevalence of a niche was found. Using contrast-enhanced sonohysterography in a random population of women with a history of CS, the prevalence was found to vary between 56% and 84%. Nine studies reported on risk factors and each study evaluated different factors, which made it difficult to compare studies. Risk factors could be classified into four categories: those related to closure technique, to development of the lower uterine segment or location of the incision or to wound healing, and miscellaneous factors. Probable risk factors are single-layer myometrium closure, multiple CSs and uterine retroflexion. Six out of eight studies that evaluated niche-related symptoms described an association between the presence of a niche and postmenstrual spotting.
  
  
  CONCLUSIONS
  The reported prevalence of a niche in non-pregnant women varies depending on the method of detection, the criteria used to define a niche and the study population. Potential risk factors can be categorized into four main categories, which may be useful for future research and meta-analyses. The predominant symptom associated with a niche is postmenstrual spotting.
authors.affiliation: Department of Obstetrics and Gynaecology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: A J M
authors.initials: AJ
authors.lastname: Bij de Vaate
authors.forename: L F
authors.initials: LF
authors.lastname: van der Voet
authors.forename: O
authors.initials: O
authors.lastname: Naji
authors.forename: M
authors.initials: M
authors.lastname: Witmer
authors.forename: S
authors.initials: S
authors.lastname: Veersema
authors.forename: H A M
authors.initials: HA
authors.lastname: Brölmann
authors.forename: T
authors.initials: T
authors.lastname: Bourne
authors.forename: J A F
authors.initials: JA
authors.lastname: Huirne
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects*; D002921:Cicatrix / Q000150:complications* / Q000453:epidemiology / Q000209:etiology; D004412:Dysmenorrhea / Q000453:epidemiology / Q000209:etiology; D005260:Female; D005298:Fertility; D006801:Humans; D008796:Metrorrhagia / Q000453:epidemiology / Q000209:etiology; D017699:Pelvic Pain / Q000453:epidemiology / Q000209:etiology; D011247:Pregnancy; D015995:Prevalence; D012307:Risk Factors; D014591:Uterine Diseases / Q000150:complications* / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology
keywords: Cesarean scar; isthmocele; postmenstrual spotting; scar defect; sonohysterography; transvaginal ultrasound; wound dehiscence