The stillbirth sex ratio as a marker of population health among live‐born males in Denmark, 1835‐1923

Objectives We know little about whether an elevated stillbirth sex ratio (ratio of male to female stillbirths) gauges stronger selection in utero against frail male gestations and therefore predicts greater male infant survival. An alternative scenario could involve a “low endowment” case in which pregnancy cohorts show both excess male stillbirths and elevated mortality risk among male live births. We exploit the longest sex‐specific stillbirth series (Denmark, 1835‐1923) to explore whether annual deviations in age‐specific male mortality vary with the annual cohort's stillbirth sex ratio. Methods We applied autoregressive, integrated, moving average time series methods to annual counts of age‐specific male mortality in Denmark. We derived the independent variable, the stillbirth sex ratio, from only late stillbirths (ie, 28th week and thereafter) owing to data availability. Methods control for secular patterns as well as shared antecedents of male and female mortality. Results Cohort male infant mortality varies positively with the stillbirth sex ratio (coef = 0.0081, standard error [SE] = 0.0019, P  < 0.001). This positive relation persists into childhood (ie, ages 1‐4.99 years) but attenuates with age. Discussion We infer support for the “low endowment” argument in that high stillbirth sex ratios predict a relatively greater risk of mortality among males which ultimately survive to birth. These findings provide evidence that the stillbirth sex ratio may serve as a marker of population health among male cohorts.