Fetal death sex ratios: a test of the economic stress hypothesis.

BACKGROUND: The ratio of male to female live births (i.e. the sex ratio) reportedly falls when populations suffer rare and extreme ambient stressors such as the collapse of national economies. This association has been attributed to the death of male fetuses and to reduced conception of males. We assess the validity of the first of these mechanisms by testing the hypothesis that the fetal death sex ratio varies positively over time with the unemployment rate. Using the unemployment rate also allows us to determine if ambient economic stressors less extreme than collapsing national economies affect the fetal death sex ratio.

METHODS: We test our hypotheses by applying time-series methods to monthly counts of fetal deaths and the unemployment rate from the state of California beginning January 1989 and ending December 2001. The methods control for trends, seasonal cycles, and other forms of autocorrelation that could induce spurious associations.

RESULTS: Results support the fetal death mechanism in that male fetal deaths increased above the values expected from female deaths and from history in months in which the unemployment rate also increased over its expected value.

CONCLUSIONS: Our findings suggest that ambient stressors as common as increasing unemployment elevate the risk of fetal death among males. We discuss the social, economic, and health costs borne by parents and communities afflicted with these fetal deaths.