Successful Pregnancy and Delivery After Detecting an Exceptionally Early-Formed Implantation Window Using Endometrial Receptivity Analysis: A Case Report

This is a report of an extremely early implantation window identified by endometrial receptivity analysis (ERA A1), in which a blastocyst was transferred onto the endometrium, resulting in a successful pregnancy and birth. An infertile couple, a 35-year-old man and a woman with nulligravida, nullipara, presented to our outpatient department with a history of 10 failed timed intercourse cycles and four unsuccessful intrauterine inseminations (IUIs) over two years. The patient exhibited ovulatory dysfunction, irregular menstruation, and polycystic ovarian syndrome. Despite initial ovarian stimulation and retrieval of good-quality blastocysts, repeated embryo transfer attempts were either canceled due to inadequate endometrial thickness or resulted in implantation failure. Consequently, an ERA was performed. Persistent ERA tests, conducted five times following repeated post-receptive results, ultimately detected an exceptionally early implantation window occurring just 67 hours after progesterone exposure. ERA-guided embryo transfers enabled implantation, but repeated attempts resulted in miscarriage, chemical pregnancy, or failure to implant. After additional oocyte retrieval and 11 embryo transfer attempts, the patient achieved a successful pregnancy and delivered a healthy baby at term. To the best of our knowledge, this case presents the world's earliest documented window of implantation with a subsequent live birth. It underscores the existence of scenarios where the timing of implantation may occur at unexpected intervals, significantly deviating from expectations based on prior knowledge and clinical experience. This report highlights the importance and practical value of ERA in managing such cases.