title: The changes in female physical and childbearing characteristics in China and potential association with risk of breast cancer.
abstract: BACKGROUND
  There has been a sharp increase in the incidence of breast cancer in China in recent years. A number of female physical characteristics, such as age at menarche, menopause, first birth and the duration of breastfeeding, have been linked to breast cancer, yet data on these factors in Chinese women is largely missing both for aggregate and age-specific data. Thus, the objective of this study was to explore changes in female menstrual and childbearing characteristics as a possible explanation for increasing rates of breast cancer in this country.
  
  
  METHODS
  From July to September 2008, a population based cross-sectional breast cancer survey covering 124,758 females from 4 provinces or cities in Eastern China was carried out, using multi-stage and cluster methods. In-person interviews based on a self-designed structured questionnaire were performed, in which female physiological and reproductive factors, such as age at menarche and menopause, menstrual cycle history, childbearing history, breastfeeding methods, abortions or miscarriage, were included. For every 10-year age category, the subjects were divided, and across those age groups, all the above factors were compared respectively and changes in physical and childbearing characteristics were evaluated. ANOVA was used to compare the differences across the groups.
  
  
  RESULTS
  A total of 122058 subjects were included in the final analysis. The mean age at menarche was 15.39 years, the mean number of full-term pregnancies was 1.58, the mean duration of breastfeeding was 22.68 months, the mean age at first birth was 23.75 years, the mean frequency of miscarriage was 0.36, and the mean age at menopause was 48.63 years. Significant differences across the several age groups were noted for the age at menarche, number of full-term pregnancies, accumulated duration of breastfeeding, age at first birth, number of miscarriages, and age at menopause. These data clearly showed a gradual shift towards an earlier age at menarche, fewer pregnancies and shorter breastfeeding lengths.
  
  
  CONCLUSIONS
  Significant changes in female physical and childbearing characteristics across a number of different age ranges were detected. These changes may be related to the increasing trend of breast cancer in China.
authors.affiliation: Department of Breast Diseases, The Second Hospital of Shandong University, Jinan, Shandong Province, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Li-yuan
authors.initials: LY
authors.lastname: Liu
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.forename: Kun
authors.initials: K
authors.lastname: Mu
authors.forename: Zhi-gang
authors.initials: ZG
authors.lastname: Yu
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001942:Breast Feeding / Q000706:statistics & numerical data; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D002681:China / Q000453:epidemiology; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D005260:Female; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D008423:Maternal Age; D008572:Menarche / Q000502:physiology*; D008875:Middle Aged; D010298:Parity / Q000502:physiology; D036801:Parturition / Q000502:physiology*; D011247:Pregnancy; D017584:Reproductive History; D012111:Residence Characteristics; D012307:Risk Factors; D011795:Surveys and Questionnaires