title: Age at Menarche, Level of Education, Parity and the Risk of Hysterectomy: A Systematic Review and Meta-Analyses of Population-Based Observational Studies.
abstract: BACKGROUND
  Although rates have declined, hysterectomy is still a frequent gynaecological procedure. To date, there has been no systematic quantification of the relationships between early/mid-life exposures and hysterectomy. We performed a systematic review and meta-analyses to quantify the associations between age at menarche, education level, parity and hysterectomy.
  
  
  METHODS
  Eligible studies were identified by searches in PubMed and Embase through March 2015. Study-specific estimates were summarised using random effects meta-analysis. Heterogeneity was explored using sub-group analysis and meta-regression.
  
  
  RESULTS
  Thirty-two study populations were identified for inclusion in at least one meta-analysis. Each year older at menarche was associated with lower risk of hysterectomy-summary hazard ratio 0.86 (95% confidence interval: 0.78, 0.95; I2 = 0%); summary odds ratio 0.88 (95% confidence interval: 0.82, 0.94; I2 = 61%). Low education levels conferred a higher risk of hysterectomy in the lowest versus highest level meta-analysis (summary hazard ratio 1.87 (95% confidence interval: 1.25, 2.80; I2 = 86%), summary odds ratio 1.51 (95% confidence interval: 1.35, 1.69; I2 = 90%)) and dose-response meta-analysis (summary odds ratio 1.17 (95% confidence interval: 1.12, 1.23; I2 = 85%) per each level lower of education). Sub-group analysis showed that the birth cohort category of study participants, the reference category used for level of education, the year the included article was published, quality of the study (as assessed by the authors) and control for the key variables accounted for the high heterogeneity between studies in the education level meta-analyses. In the meta-analyses of studies of parity and hysterectomy the results were not statistically significant.
  
  
  CONCLUSIONS
  The present meta-analyses suggest that the early life factors of age at menarche and lower education level are associated with hysterectomy, although this evidence should be interpreted with some caution due to variance across the included studies.
authors.affiliation: The University of Queensland, Centre for Longitudinal and Life Course Research, School of Public Health, Public Health Building, Herston Road, Herston, Queensland, 4006, Australia.
authors.forename: Louise F
authors.initials: LF
authors.lastname: Wilson
authors.affiliation: The University of Queensland, Centre for Longitudinal and Life Course Research, School of Public Health, Public Health Building, Herston Road, Herston, Queensland, 4006, Australia.
authors.forename: Gita D
authors.initials: GD
authors.lastname: Mishra
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004522:Educational Status; D005260:Female; D006801:Humans; D007044:Hysterectomy; D008572:Menarche / Q000502:physiology*; D008875:Middle Aged; D010298:Parity / Q000502:physiology*; D012307:Risk Factors; D055815:Young Adult