Presence of endometrial nucleolar channel systems at the time of frozen embryo transfer in hormone replacement cycles with successful implantation

Objective: To detect nucleolar channel systems (NCSs) in cells in endometrial aspirations obtained immediately before embryo transfer during blastocyst hormone replacement therapy-frozen embryo transfer (HRT-FET) cycles without affecting implantation. Design: Prospective case series. Setting: University-affiliated fertility clinic. Patient(s): Five patients who underwent an HRT-FET cycle consented to lower uterine segment aspiration using an open-tip embryo transfer catheter during a routine mock transfer performed immediately before embryo transfer. Intervention(s): Exfoliated cells in the aspirated endometrial secretions were analyzed for the presence of NCSs using indirect immunofluorescence and, in one case, electron microscopy for unambiguous identification. Main Outcome Measure(s): On the basis of a previous study, positive NCS status was defined as the presence of NCSs in at least 3 endometrial epithelial cells (EECs). The effect of endometrial aspiration on implantation and pregnancy outcomes was assessed. Result(s): Biochemical pregnancy, as evidenced by positive β-human chorionic gonadotropin, was seen in 5 of 5 patients, and clinical pregnancy was seen in 2 of 5 patients. NCSs were detected in exfoliated EECs of uterine secretions in 4 of 5 patient samples and could not be unequivocally identified in 1 of 5 patient samples, which was designated as indeterminate. Conclusion(s): This is the first report of NCS detection in HRT-FET cycles in the absence of follicular development and ovulation. NCS status can be determined in exfoliated EECs of uterine secretions obtained at the time of embryo transfer while maintaining implantation. Our study furthers the goal of establishing whether individualized point of care testing of NCS status in HRT-FET cycles can determine optimal endometrial receptivity and improve pregnancy outcomes.