Pinopodes as markers of endometrial receptivity in clinical practice

Clinical evidence indicates the existence in the human of a narrow window of uterine receptivity which opens during the mid-luteal phase. At the same time, formation of pinopodes on the apical membranes of the endometrial epithelial cells occurs. To develop a specific marker for receptivity in clinical practice, the kinetics of pinopode formation has been investigated through sequential endometrial biopsying in natural, hormone replacement and stimulated cycles. The results show that pinopodes last <48 h in all cycles, and the timing of their formation depends both on the hormonal treatment applied and on the patient's individual response. On average, pinopodes form earlier in stimulated cycles and later in hormone replacement cycles, compared with natural cycles. Pinopode expression is strongly correlated with implantation following embryo transfer and furthermore, detection of pinopodes in assessment cycles may be extremely useful for the assessment of receptivity on an individual basis to optimize embryo transfer, resulting in increased implantation rates. Finally, pinopodes seem to be correlated well with other cellular and molecular events occurring in the mid-luteal endometrium.