Case Report: Sequential blastocyst transfer for women with unexplained recurrent implantation failure: a case series.

Background: Repeated implantation failure (RIF) is a frustrating situation for patients and medical physicians. In spite of extensive research, the underlying mechanisms of RIF are not fully understood. Endometrial receptivity is considered a critical factor for embryo implantation, particularly in patients with unexplained RIF who have usable embryos. Sequential embryo transfer (ET) has been demonstrated to improve clinical pregnancy rates in RIF patients by optimizing embryo-endometrium synchronization and interaction. In this study, we propose a strategy of sequential blastocyst transfer within a single frozen embryo transfer cycle to improve Case presentation: Three women under 40 years of age had undergone repeated failed embryo transfer cycles in our hospital. Based on ESHRE recommendations for RIF investigation, no significant causative or contributory factors were identified, apart from mild intrauterine adhesion or chronic endometritis, treated before embryo transfer. Further embryo transfers still failed, even with regular sequential cleavage/blastocyst transfer. However, all three patients achieved positive clinical pregnancies with sequential blastocyst embryo transfer. Two of the patients had live births and the remaining patient experienced an early spontaneous miscarriage for which a pathogenic deletion of chromosome 21 was identified. Conclusion: Repeated implantation failure is a complex, challenging, and burdensome condition, which causes considerable psychological and physical suffering for patients and reproductive specialists. Sequential blastocyst transfer is a potential option for patients with unexplained RIF undergoing IVF.