Life Course Variation in the Relation Between Maternal Marital Status and Preterm Birth

PurposeMaternal marriage is protective against preterm birth (PTB), whereas advanced maternal age is associated with increased PTB risk. Because relations between social factors and health may vary during the life course, we assessed how the relation between marital status and PTB risk may change with maternal age.MethodsWe assessed the interaction between marital status and maternal age as a determinant of PTB among all live singleton births in Michigan between 1995 and 2006. We also fit stratified models by race. We calculated absolute differences in predicted PTB as well as odds ratios of PTB by marital status for each age group.ResultsIn adjusted models, there was a significant interaction (pinteraction<.001) between marital status and maternal age. The predicted probability of PTB by marital status was marginally different among mothers ages 20–25 years (absolute difference of 1.5%); this difference was substantially greater (3.9% or greater) after 31 years of age. Odds of PTB followed a similar trajectory. Findings were similar among black and white mothers.ConclusionsThe relationship between marriage and PTB may vary with maternal age suggesting that the influence of social factors on risk for adverse birth outcomes may differ through the maternal life trajectory. We discuss plausible explanations for these findings.