title: Factors associated with spontaneous abortion: a cross-sectional study of Chinese populations.
abstract: BACKGROUND
  Spontaneous abortion (SA) is one of the prevalent negative reproductive outcomes among women around the world, which is a great challenge faced by maternal health promotion. The present study is aimed to explore the association between SA and socioeconomic status (SES) and provides reference for policy makers to improve strategies on maternal health promotion.
  
  
  METHODS
  A cross-sectional analysis was conducted with baseline data from a large-scale population-based cohort study of 0.5 million people from 10 geographically diverse areas of China recruited from 2004 to 2008. The study collected data from 84,531 women aged 35-45 years old in the baseline survey of China Kadoorie Biobank. Participants were interviewed using a standardized questionnaire, and information on demographic-socioeconomic as well as reproductive health status was collected. Odds ratios (OR) with 95% CI, estimated by a multistep logistic regression, were used to approximate the associations between SA occurrence and characteristics of SES. A stratification analysis was also applied to find out how SES influenced women's reproductive health outcomes differently between rural and urban areas. The model was adjusted for age at study date, tea consumption, alcohol consumption, cigarette smoking, and number of induced abortion.
  
  
  RESULTS
  The risk of SA in rural was 1.68 times greater than in urban (AOR = 1.68, 95%CI: 1.54-1.84). Women with high income had a decreased risk of SA when compared with that of women with low income (AOR = 0.90, 95%CI: 0.84-0.97). Compared with women in low educational attainment, women in higher educational attainment had a lower prevalence of SA (AOR = 0.90, 95%CI: 0.82-0.98). The risk of SA only reduced in factory worker (AOR = 0.59, 95%CI: 0.53-0.66) and professional worker (AOR = 0.75, 95%CI: 0.66-0.84) compared with agriculture and related workers. After stratifying by rural/urban, the association between income and SA in urban (AOR = 0.88, 95%CI: 0.78-0.99) was stronger than that in rural (AOR = 0.92, 95%CI: 0.84-1.00). Association between education and SA was found in urban (AOR = 0.66, 95%CI: 0.55-0.78) but not in rural (AOR = 1.05, 95%CI: 0.34-1.17), and there was no difference on how occupation impacted SA among women between the two subgroups.
  
  
  CONCLUSIONS
  Generally women with lower SES status had a higher risk of SA. Lower income and educational attainment were inversely associated with the risk of SA. Women with agricultural and related work had a significantly higher prevalence of SA. Interventions could be targeted more on women with low SES to increase both health profits as well as economic gains for health programs.
authors.affiliation: Department of Global Health, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Danni
authors.initials: D
authors.lastname: Zheng
authors.affiliation: Department of Global Health, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Li
authors.affiliation: School of Basic Medical Science, Peking University, Beijing, 100191, China.
authors.forename: Taiwen
authors.initials: T
authors.lastname: Wu
authors.affiliation: Department of Global Health, School of Public Health, Peking University, Beijing, 100191, China. tangkun@hsc.pku.edu.cn.
authors.forename: Kun
authors.initials: K
authors.lastname: Tang
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology*; D000328:Adult; D002681:China; D003430:Cross-Sectional Studies; D005260:Female; D006293:Health Promotion; D006801:Humans; D008875:Middle Aged; D015995:Prevalence; D012307:Risk Factors; D012424:Rural Population; D012959:Socioeconomic Factors; D014505:Urban Population
keywords: China Kadoorie Biobank; Maternal health; Socioeconomic status; Spontaneous abortion