Fertilization and early pregnancy loss in healthy women attempting conception.

The rosette inhibition test was used to monitor the activity of an early pregnancy factor (EPF) in sera collected from 18 healthy women who were attempting to conceive. Serial blood samples collected during the luteal phase of 21 menstrual cycles demonstrated the appearance of EPF in 14 of the cycles, of which six showed only transient EPF activity over a 5-10 day period following ovulation. These results indicate a 67% rate of fertilization and a 36% rate of early conceptus losses.