Influence of superovulation on endometrial and embryonic development.

The authors have studied the temporal relationship between follicular rupture and endometrial development in 13 women during a natural ovarian cycle (length 25 to 35 days), and subsequently after standard treatment with clomiphene citrate, human menopausal gonadotropin and human chorionic gonadotropin (hCG) to induce multiple folliculogenesis for oocyte recovery, in vitro fertilization, and embryo freezing (cycle length 23 to 27 days). An endometrial biopsy was taken during both cycles 1.5 to 2.0 days after the oocytes had been released or removed. The samples were examined by light and transmission electron microscopy. Samples of peripheral blood were taken at defined times for hormone analysis. After treatment 11 subjects (85%) had advanced morphological development of the endometrium (8 women by 3 to 4 days, 3 women by 1 to 2 days). The concentrations of plasma estradiol (E2) and progesterone (P) on the days of follicular rupture and endometrial biopsy were significantly raised in the treatment cycles. The concentration of total urinary estrogens on the day of hCG administration and the mean change in the concentration of plasma E2 (treatment/control) on the days of endometrial biopsy were positively correlated with the extent of endometrial advancement. In addition, the mean change in the concentration of plasma P (treatment/control) was markedly increased on the days of follicular rupture and endometrial biopsy in those subjects with an advanced endometrium. Embryonic development was not so obviously related to the extent of superovulation. Asynchronous endometrial and embryonic development may therefore contribute to the low pregnancy rate in these patients.