Background A reduction in sex ratio at live birth has been proposed as a sentinel health indicator that can be used to monitor the health of populations.

Objective To test the hypothesis that a lower sex ratio is associated with adverse national population health using the prevalences of HIV and tuberculosis as measures of societal well-being.

Methods An ecological study design using routinely collected data and adjusting for potential confounding factors.

Results The mean global sex ratio was 1.05. There was marked heterogeneity in the sex ratio between different global regions (p<0.0001). Those regions with the highest prevalences of HIV infection had lower sex ratios, with the value for the highest quartile being 0.022 (95% CIs CI 0.013 to 0.031) lower than the lowest quartile. Similarly, those areas with the highest quartile of tuberculosis infection had a sex ratio of 0.016 (95% CI 0.004 to 0.028) lower than those in the lowest quartile. Similar results were observed in a subgroup analysis limited to countries from the African continent.

Conclusions The data are consistent with the hypothesis that a reduced sex ratio at live birth is a potential sentinel health indicator of lower population health. However, these data do not demonstrate either a casual relationship or reveal any biological mechanisms that may account for these observations.