Sex Ratio Trends

One family I know of is very concerned about excess c-sections. I have only followed their reasoning from a distance, but I've always wanted to follow it more. In light of their worries about the negative implications of rising c-sections, I thought this was interesting. A very interesting new article entitled "The rise and fall of excess male infant mortality" finds the following:

"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."

Here's one quote from the article:

"In the last several decades, medical-technical advances, such as the increased use of Cesarean deliver y (C-section) and the spread of neonat al intensive care units (NICUs), have further lowered infant mortality, particularly among small and premature babies, which would disproportionately benefit males."

Sex ratios at birth tend to be skewed. On the one hand, there's a slightly higher probability of a male birth, making it not entirely a coin flip. But, on the other hand, the male child has a lower survival rate than the female, meaning that in developing countries or areas with poor access to neonatal healthcare, you'll see higher infant mortality but which selects on males more often, which offsets the slightly higher chances of a male birth. C-sections and other neonatal technological advances in healthcare appear to have benefited the male survival chances, and caused sex ratios to change.