Socioeconomic inequality in preterm birth in four Brazilian birth cohort studies

Objective: To analyze economic inequality (absolute and relative) due to family income in relation to the occurrence of preterm births in Southern Brazil. Methods: Four birth cohort studies were conducted in the years 1982, 1993, 2004, and 2011. The main exposure was monthly family income and the primary outcome was preterm birth. The inequalities were calculated using the slope index of inequality and the relative index of inequality, adjusted for maternal skin color, education, age, and marital status. Results: The prevalence of preterm births increased from 5.8% to approximately 14% (p‐trend