Lag in endometrial morphology in artificially reproduced cycles (ARC).

To observe if endometrial artificially reproduced cycles were identical to the natural spontaneous ones, we have matched for the endometria of 22 assessed spontaneous ovulating women and 16 postmenopausal ones sequentially treated with exogenous ovarian steroid hormones. The endometrial samples were drawn in the middle luteal phase (20th-22nd of an ideal cycle, 6-8 days from ultrasound assessed ovulation or progesterone exposure), because this is the "implantation window" period. These results can be particularly interesting in the FIV-OD technique that implyes the implantation of the zygote in a fully matured endometrium. Adversely to previous reports there was always an endometrial hystologic lag (2 min.-4 max. days) in all the artificially reproduced cycles observed, while no other endometrial anomalies were found in these last ones. Probably the contrasting results of the previous studies agree with the later timing of endometrial biopsy, because in the late luteal artificially reproduced or spontaneous endometrium there is no hystological difference.