The gestational timing of pregnancy loss: adaptive strategy?

This commentary links early pregnancy milestones (rescue of the corpus luteum, the luteal-placental shift, and blocking of the spiral arteries) with the pattern of gestation-specific pregnancy loss in humans. The objective is to describe the pattern and present an adaptive hypothesis: that high first trimester pregnancy loss results from selection to reduce the risk of maternal morbidity and mortality associated with human delivery. Specific questions within the broad framework of this hypothesis can be addressed with research in comparative physiology and endocrinology.