title: Changes in the relationship between marriage and preterm birth, 1989-2006.
abstract: OBJECTIVE
  Maternal marriage has historically been protective against preterm birth (PTB); however, social norms and behaviors surrounding marriage have changed over time in the United States. We analyzed secular trends in the relationship between marriage and PTB.
  
  
  METHODS
  We collected data about all births in Michigan between 1989 and 2006 to assess (1) the relationship between marital status and PTB and moderately PTB risk by year, and (2) the relationship between married and unmarried status and PTB and moderately PTB by year relative to similar marital status in 1989.
  
  
  RESULTS
  Among nearly 2.4 million births between 1989 and 2006, PTB risk among married mothers increased while risk among unmarried mothers decreased. In adjusted models, married status became less protective against PTB relative to unmarried status over time by year, and was associated with higher risk of PTB over time. Moderately PTB risk increased among both married and unmarried groups, but more so among married mothers.
  
  
  CONCLUSIONS
  Our findings suggest that marriage is becoming less protective against PTB over time. The influence of social factors on risk for adverse birth outcomes is likely dynamic, suggesting that ongoing revisions to our understanding are in order.
authors: Columbia University, Mailman School of Public Health, Department of Epidemiology, New York, NY, USA. ame2145@columbia.edu
authors: Abdulrahman M
authors: AM
authors: El-Sayed
authors: Sandro
authors: S
authors: Galea
mesh_terms: D000328:Adult; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007086:Illegitimacy / Q000706:statistics & numerical data; D007231:Infant, Newborn; D007234:Infant, Premature; D008393:Marriage / Q000706:statistics & numerical data*; D008824:Michigan / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth; D018570:Risk Assessment; D012307:Risk Factors