Extreme maternal education and preterm birth: time-to-event analysis of age and nativity-dependent risks

Purpose: Increasing numbers of women achieve extremely high education, but the association with preterm birth (PTB) is poorly understood, especially over the life course. We sought to determine how very high educational attainment is associated with PTB, and to assess differences by maternal age and nativity. Methods: Data included singleton live births to mothers aged >= 20 years in metropolitan areas of Quebec, Canada, from 1995 to 2005 (n = 537,525). Hazard ratios of PTB (<37 gestational weeks) were estimated over the continuous range of education (0-30 years) according to maternal age (20-24, 25-29, 30-34, >= 35 years) and nativity in a flexible survival model. Results: The relationship between education and PTB was not linear, but suggested that extremely high education was not as protective against PTB as slightly lower education. Education thresholds that offered maximum protection increased with maternal age, and were lower for Canadian-born (17-21 years of education) than foreign-born (22-25 years of education) mothers. Conclusions: Extremely high education did not confer more protection against 131-13 than slightly lower education, and associations varied over the life course. The threshold number of years of education most protective against PTB: (1) increased with maternal age, especially for Canadian-born mothers, and (2) was higher for foreign-born mothers. (C) 2013 Elsevier Inc. All rights reserved.