The rise and fall of excess male infant mortality

Abstract

The male disadvantage in infant mortality underwent a surprising rise and fall in the 20th century. Our analysis of 15 developed countries shows that, as infant mortality declined over two centuries, the excess male mortality increased from 10% in 1751 to >30% by approximately 1970. Remarkably, since 1970, the male disadvantage in most countries fell back to lower levels. The worsening male disadvantage from 1751 until 1970 may be due to differential changes in cause-specific infant mortality by sex. Declines in infant mortality from infections and the shift of deaths to perinatal conditions favored females. The reduction in male excess infant mortality after 1970 can be attributed to improved obstetric practices and neonatal care. The additional male infants who survived because of better conditions were more likely to be premature or have low birth weight, which could have implications for their health in later life. This analysis provides evidence of marked changes in the sex ratio of mortality at an age when behavioral differences should be minimal.

Fig. 1.

q₀^M/q₀^F averaged over 10-year intervals, 1751–2004, for each of the 15 countries and for all countries available at a given date (left axis). Average over 10-year intervals of, q₀^M and q₀^F for all countries available in each time period (right axis). Data source: Human Mortality Database (www.mortality.org).

Fig. 2.

Scatterplot of infant mortality (q₀) versus sex ratio of infant mortality (q₀^M/q₀^F) for 15 countries averaged over 10-year intervals. Data source: Human Mortality Database (www.mortality.org). q₀^M/q₀^F was regressed on q₀ for both sexes combined. When q₀ ≥ 0.02, R² is 66%. When q₀ < 0.02 (dark vertical line), the relationship between q₀ and the sex ratio of infant mortality largely disappears (R² = 20%).

Fig. 3.

Proportion of infant deaths attributable to specified causes of death (left axis), U.S., 1921–1993. Annual sex ratio of infant mortality (q₀^M/q₀^F, right axis). Dark vertical lines separate periods covered by revisions of the International Classification of Disease. For data sources, see references in SI Text.

Fig. 4.

Neonatal mortality rates by sex and birth weight (left axis) and male (M)/female (F) neonatal mortality ratios by birth weight (right axis), U.S. 1950 and 2000. For data sources, see references in SI Text.

Fig. 5.

Historical increases in Cesarean delivery for 15 countries, 1955–2003. For data sources, see references in SI Text.