Fig. 3
Minimally (A) and country-specific fully (B) adjusted odds ratios of preterm birth by maternal age group and marital status in Brazil, Ecuador, USA, and Canada. † Adjusted for infant sex, previous birth, and year of birth. ‡ Brazil: Adjusted for infant sex, previous birth, year of birth, paternal age, maternal race, prenatal care initiated in 1st trimester, state, and age-appropriate low education. Ecuador: Adjusted for infant sex, previous birth, year of birth, maternal ethnicity, foreign-born mother, adequacy of the number of prenatal care visits for gestational age (WHO), maternal literacy, and maternal region of residence and rurality. USA: Adjusted for infant sex, previous birth, year of birth, paternal age, maternal race/ethnicity, foreign-born mother, any maternal smoking during pregnancy, prenatal care adequacy (GINDEX), received WIC during pregnancy, and delivery primarily paid by Medicaid. Canada: Adjusted for infant sex, previous birth, year of birth, paternal age, foreign-born mother, foreign-born father, province/territory of birth, reside in rural or urban area, and area-level income quintiles. ***p < 0.0001, **p < 0.01, *p < 0.05 for difference in odds ratios between married and unmarried mothers within age group