UTERINE PINOPODES AS MARKERS OF THE NIDATION WINDOW IN CYCLING WOMEN RECEIVING EXOGENOUS ESTRADIOL AND PROGESTERONE

In 14 cycling women participating in an in-vitro fertilization (IVF) d onation programme, we examined the timing of the 'nidation window' usi ng as a stage-specific 'marker' the presence of fully developed pinopo des on the apical surface of the luminal uterine epithelium. Each woma n received exogenous oestradiol from the second day of their cycle and progesterone starting on day 8 or day 15 of the oestrogenic treatment . The women underwent two biopsies during the same artificial cycle, o n either days 6 and 9 or days 8 and 10 of the progesterone treatment. All patients to whom oestradiol was administered for 7 days prior to p rogesterone administration (n = 9), and two of the five treated with o estradiol for 14 days prior to the addition of progesterone, showed ut erine pinopodes in either one or both biopsies. When present on a give n day, pinopodes were at the same stage, developing, fully developed o r regressing, showing that their total lifespan did not exceed 48 h. F ully developed pinopodes existed for 1 day only which may correspond t o the short period of optimal endometrial receptivity observed in anim al models. The timing of the presence of fully developed pinopodes var ied from patient to patient, but these individual differences were not correlated with progesterone and oestradiol plasma concentrations. Th e brief duration of the nidation window and the observed individual va riations in its timing suggest that the detection of uterine pinopodes could be a valuable tool for the prediction, on an individual basis, of the optimal date for successful egg replacement in IVF patients.