Hormonal evidence of selection in utero revisited

Human conception cohorts in gestation during stressful times reportedly yield lower ratios of male to female live births than do other conception cohorts. Much literature attributes this phenomenon to spontaneous abortion of less fit male fetuses. Controversy remains, however, as to whether stressful times make males fetuses less fit ("Shifting Distribution" of fitness) or whether male fetuses need greater fitness to avoid spontaneous abortion during stressful times ("Shifting Criterion" for survival).

Although research using gestational hCG as a signal of fetal fitness reports support for the latter mechanism, we believe an analytic error casts doubt on those findings. Here we offered an alternative test that corrects the error.

This more accurate test found similar results to those originally reported.