Uterine pinopodes in peri-implantation human endometrium. Clinical relevance

Current clinical studies indicate the existence in the human of an "implantation/nidation window," similar to that observed in animal models. During this short period of uterine receptivity, the formation of pinopodes on the apical cell membrane of the endometrial epithelium is a consistent morphological event, observed in a number of species studies including the human. In order to develop a specific marker of the implantation window in clinical practice, we have investigated the kinetics of pinopode formation through sequential endometrial sampling under various hormonal conditions. Our results show that the implantation window in humans, according to this marker, lasts less than 48 hours, and the timing of its opening is dependent on the hormonal treatment applied, occurring earlier in cycles following ovarian stimulation and later in cycles induced by hormone replacement treatment. Furthermore, the timing varies among different individuals under the same treatment. These findings suggest that examination for pinopodes in endometrial samples can be highly useful in infertility treatment and research for the assessment of the nidation window on an individual basis. Our preliminary data strongly support the value of this assessment for better timing of ovum transfer, leading to an increase in implantation rates. Studies are now in progress on the expression of other endometrial signals present in relation to the pinopodes.