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 (7) 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.
Conclusion.
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.
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