title: Parity and osteoporotic fracture risk in postmenopausal women: a dose-response meta-analysis of prospective studies.
abstract: The present dose-response meta-analysis shows linearly decreased hip fracture (HF) risk and nonlinearly decreased osteoporotic fracture (OF) risk associated with increasing number of parity of up to five live births among postmenopausal women.
  
  
  BACKGROUND
  Epidemiological reports suggest that parity is associated with reduced OF risk among women. However, these findings are controversial. Here, we present a meta-analysis of prospective studies of parity in relation to OF risk.
  
  
  METHODS
  We performed systematic searches using Medline and Embase from January 1, 1966, to December 31, 2014, with limits of language in English and prospective study design. Relative risks (RRs) and confidence intervals (CIs) were derived mainly using random-effects models. Categorical, dose-response, heterogeneity, publication bias, and subgroup analyses were conducted.
  
  
  RESULTS
  We analyzed 10 articles of 19 independent reports from 1966 to 2014, comprising a total of 217,295 participants and 26,525 cases of OF. Compared to nulliparous women, the OF and HF risks of parous women with at least one live birth were reduced by 11 % (95 % confidence interval (CI) 3-19 %; I (2) = 77.1 %, p < 0.001) and 26 % (95 % CI 17-35 %; I (2) = 19.5 %, p = 0.287), respectively. Representative nonlinearly and linearly inverse dose-response associations were found between parity (range of 0-6) and OF risk (p nonlinearity = 0.0163; I (2) = 79.7 %, p < 0.001), and between parity (range of 0-5) and HF risk (p nonlinearity = 0.054; I (2) = 76.5 %, p < 0.001), respectively. The lowest risk reduction for OF of 25 % (95 % CI 16-33 %) was observed for five live births. And, the summary risk reduction for HF was 12 % (95 % CI 9-15 %) for each one increased live birth.
  
  
  CONCLUSIONS
  We found that increasing number of parity is associated with linearly reduced HF risks among women. The association between parity of six or more live births and HF risks should be studied further in future.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China.
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Medical Rehabilitation, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China.
authors.forename: Q
authors.initials: Q
authors.lastname: Huang
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Department of Occupational Hygiene, Wuhan Hospital for the Prevention and Treatment of Occupational Diseases, Wuhan, Hubei Province, China.
authors.forename: J-J
authors.initials: JJ
authors.lastname: Liang
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China.
authors.forename: S-Y
authors.initials: SY
authors.lastname: Liu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China.
authors.forename: X
authors.initials: X
authors.lastname: Gu
authors.affiliation: Department of Social Medicine and Health Management, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei Province, China. lja10_11@163.com.
authors.forename: J-A
authors.initials: JA
authors.lastname: Liu
mesh_terms: D005260:Female; D006620:Hip Fractures / Q000453:epidemiology / Q000517:prevention & control; D006801:Humans; D015663:Osteoporosis, Postmenopausal / Q000453:epidemiology / Q000517:prevention & control; D058866:Osteoporotic Fractures / Q000453:epidemiology* / Q000517:prevention & control; D010298:Parity; D011446:Prospective Studies; D018570:Risk Assessment / Q000379:methods
keywords: Fracture; Hip; Meta-analysis; Osteoporosis; Parity; Women