Associations Between Sex Composition of Older Siblings and Infant Mortality in India from 1992 to 2016

Background: This study examines associations between sex composition of older siblings and infant mortality by sex, to guide efforts to address excess female infant mortality in India.

Methods: We conducted a retrospective cross-sectional study of infant mortality in India using four waves of data from the nationally-representative National Family Health Survey, collected between 1992 and 2016 (unweighted N = 338,504 for children aged 1-5). We used sex-stratified multivariable logistic regression models to assess the associations between sex composition of older siblings and risk of infant mortality.

Findings: Male infants with two living older sisters and no living older brothers had lower odds of infant mortality relative to those with one living older brother (e.g., 2015-16 AOR 0.62, 95% CI 0.50-0.76); this effect was significant for boys across all waves of data but was not seen for girls in any wave. Exploratory models focused on third order births found that boys were less likely than girls to die in infancy if born subsequent to two older sisters (2015-16 AOR 0.48, 95% CI 0.31-0.74); analysis of crude prevalence data indicated that this converts into a 64% greater risk for infant mortality for girls relative to boys in this third-order group.

Interpretation: Higher birth order males with older sisters have greater protection against infant mortality, a finding that has persisted for over 25 years. To address ongoing gender inequities in infant survival in India, greater focus is needed to support higher birth order girls and social norm movements against son preference.