title: Parity and pancreatic cancer risk: a dose-response meta-analysis of epidemiologic studies.
abstract: BACKGROUND
  Previous epidemiologic studies have reported inconsistent results between parity and pancreatic cancer (PC) risk. To our knowledge, a comprehensive and quantitative assessment of this association has not been conducted.
  
  
  METHODS
  Relevant published studies of parity and PC were identified using MEDLINE (PubMed) and Web of Science databases until November 2013. Two authors (H-BG and LW) independently assessed eligibility and extracted data. Eleven prospective and 11 case-control studies reported relative risk (RR) estimates and 95% confidence intervals (CIs) of PC associated with parity. Fixed- and random-effects models were used to estimate the summary RR depending on the heterogeneity of effects.
  
  
  RESULTS
  The summary RR for PC comparing the highest versus lowest parity was 0.86 (95% CI: 0.73-1.02; Q = 50.49, P<0.001, I2 = 58.4%). Significant inverse associations were also observed in the studies that adjusted for cigarette smoking (RR = 0.81; 95% CI: 0.68-0.98), Type 2 diabetes mellitus (RR = 0.83; 95% CI: 0.75-0.93), and those that included all confounders or important risk factors (RR = 0.85; 95% CI: 0.76-0.96). Additionally, in the dose-response analysis, the summary RR for per one live birth was 0.97 (95% CI: 0.94-1.01; Q = 62.83, P<0.001, I2 = 69.8%), which also indicated a borderline statistically significant inverse effect of parity on PC risk. No evidence of publication bias and significant heterogeneity between subgroups were detected by meta-regression analyses.
  
  
  CONCLUSIONS
  In summary, these findings suggest that higher parity is associated with a decreased risk of PC. Future large consortia or pooled studies are warranted to fully adjust for potential confounders to confirm this association.
authors.affiliation: Department of Obstetrics and Gynecology, Shengjing Hospital, China Medical University, Shenyang, China.
authors.forename: Hong-Bo
authors.initials: HB
authors.lastname: Guan
authors.affiliation: Center for Clinical and Translational Science, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Lang
authors.initials: L
authors.lastname: Wu
authors.affiliation: Department of Epidemiology, Shanghai Cancer Institute, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China; State Key Laboratory of Oncogene and Related Genes, Shanghai Cancer Institute, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Qi-Jun
authors.initials: QJ
authors.lastname: Wu
authors.affiliation: Department of Educational Psychology, University of Minnesota, Minneapolis, Minnesota, United States of America.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Obstetrics and Gynecology, Shengjing Hospital, China Medical University, Shenyang, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Gong
mesh_terms: D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016017:Odds Ratio; D010190:Pancreatic Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D010298:Parity; D011247:Pregnancy; D011446:Prospective Studies; D012306:Risk