title: Multiple births and risk of epithelial ovarian cancer.
abstract: METHODS
  Prevailing hypotheses about the causes of ovarian carcinogenesis predict that women with a history of multiple births (twins, triplets, etc.) should be at increased risk of epithelial ovarian cancer. However, the scant available evidence suggests that they may actually be at lower risk. To resolve this issue, we pooled data from eight studies involving 2859 parous women with epithelial ovarian cancer (case patients) and 7434 parous women without ovarian cancer (control women). In addition to assessing their history of multiple births (and the sex of the children, where available), we obtained information on age, parity, oral contraceptive use, and other reproductive factors for each woman. Details of tumor histology were available for all case patients. We estimated the relative risks of various histologic types of ovarian cancers associated with multiple births by using multivariable logistic regression analysis, adjusting for matching and confounding variables.
  
  
  RESULTS
  Among these parous women, 73 case patients (2. 6%) and 257 control women (3.5%) had a history of multiple births. The adjusted summary odds ratio (OR) for developing all types of epithelial ovarian cancer that are associated with multiple births was 0.81 (95% confidence interval [CI] = 0.61-1.08). We found no evidence that risks associated with multiple births differed among women with borderline or invasive tumors and among women with same-sex and opposite-sex offspring from multiple births. The risk reductions appeared specific for nonmucinous tumors (n = 2453; summary adjusted OR = 0.71 [95% CI = 0.52-0.98]); in contrast, associations with mucinous tumors (n = 406) were heterogeneous across studies.
  
  
  CONCLUSIONS
  Parous women with nonmucinous ovarian cancer are no more likely to have a history of multiple births than other parous women, counter to the predictions of current hypotheses for causes of ovarian cancer.
authors.affiliation: Imperial Cancer Research Fund General Practice Research Group, University of Oxford, U.K. daveW@qimr.edu.au
authors.forename: D C
authors.initials: DC
authors.lastname: Whiteman
authors.forename: M F
authors.initials: MF
authors.lastname: Murphy
authors.forename: L S
authors.initials: LS
authors.lastname: Cook
authors.forename: D W
authors.initials: DW
authors.lastname: Cramer
authors.forename: P
authors.initials: P
authors.lastname: Hartge
authors.forename: P A
authors.initials: PA
authors.lastname: Marchbanks
authors.forename: P C
authors.initials: PC
authors.lastname: Nasca
authors.forename: R B
authors.initials: RB
authors.lastname: Ness
authors.forename: D M
authors.initials: DM
authors.lastname: Purdie
authors.forename: H A
authors.initials: HA
authors.lastname: Risch
mesh_terms: D002288:Adenocarcinoma, Mucinous / Q000453:epidemiology; D000328:Adult; D000368:Aged; D001315:Australia / Q000453:epidemiology; D002277:Carcinoma / Q000453:epidemiology* / Q000209:etiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D009099:Multiple Birth Offspring; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D010051:Ovarian Neoplasms / Q000453:epidemiology* / Q000209:etiology; D012306:Risk; D014481:United States / Q000453:epidemiology