Socioeconomic inequalities in infant mortality in Colombia: a nationwide cohort study during 10 years.

Background: Although socioeconomic inequalities in infant mortality are well-documented globally, there is limited evidence from longitudinal studies, particularly in low-income and middle-income countries. This study investigates the association between maternal socioeconomic conditions, health system affiliation and infant mortality, and it measures the related socioeconomic inequalities in Colombia over a decade.

Methods: A retrospective cohort study was conducted using data from the Unified Affiliation Registry on all singleton live births in Colombia from 1 January 2011 to 31 December 2020. Birth and death records were linked using anonymised maternal IDs. The primary outcome was 1-year survival. Key exposures included maternal educational level, health system enrolment scheme and area of residence. Cox regression models were used to estimate HRs, adjusting for relevant covariates. The Relative Index of Inequality (RII) and the Slope Index of Inequality (SII) were also calculated.

Findings: Among the 5 951 953 live births recorded, 5 605 111 were analysed. Significant inequalities were noted based on maternal education, health system affiliation and area of residence. Children of mothers with primary or lower education had a 50% higher risk of dying in the first year (adjusted HR (aHR) 1.50; 95% CI 1.44 to 1.56). Those with uninsured mothers had a 61% higher risk compared with those with mothers in the contributory health scheme (aHR 1.61; 95% CI 1.54 to 1.68). Additionally, children of mothers in dispersed rural areas had an 8% higher risk of first-year mortality compared with those in urban municipal centres (aHR 1.08; 95% CI 1.05 to 1.11). There was a clear pattern of social gradients in infant mortality (educational level: RII 1.55, 95% CI 1.49 to 1.62, and SII 4.12, 95% CI 3.76 to 4.48; health insurance scheme: RII 1.67, 95% CI 1.60 to 1.73 and SII 4.78, 95% CI 4.42 to 5.14; residence's zone: RII 1.12, 95% CI 1.07 to 1.17 and 1.04, 95% CI 0.63 to 1.44) and a notable increasing trend in educational inequalities (The RII and SII revealed increasing from 2011 to 2020 (RII from 1.18 to 1.92; SII from 1.59 to 5.74)).

Interpretation: Despite Colombia's economic growth, the persistence and increase of socioeconomic inequalities in infant mortality found in this analysis highlight the need for comprehensive policy reforms targeting healthcare access and socioeconomic conditions.