Endometrial biopsy during a cycle of conception.

Endometrial biopsies obtained from 18 infertile women during early intrauterine pregnancy were examined histologically. The cycle date on which the biopsies were obtained was determined from the day of ovulation by basal body temperature charts and prior menstrual history. The average cycle dates of the biopsies were similar for the women who delivered at term or who had first-trimester spontaneous abortions. Among the women who delivered at term, the average histologic date assigned to the specimens was significantly earlier than the average cycle date. In contrast, among the women who had early pregnancy loss, the specimens had an average histologic date significantly later than the average cycle date. A histologic date of later than 25 days or later than the cycle date of the biopsy was associated with a poor prognosis for the pregnancy.