The goal of this clinical trial aims to investigate whether a non-invasive implantation window prediction model, constructed based on characteristic changes in peripheral blood miRNAs during the peri-implantation period, can improve pregnancy outcomes in patients with unexplained recurrent implantation failure undergoing frozen embryo transfer. Researchers will compare the clinical pregnancy outcomes between individualized embryo transfer guided by implantation window results and conventional embryo transfer, to observe whether implantation window-guided individualized embryo transfer can improve the clinical efficacy for patients with recurrent implantation failure (RIF). Participants will complete implantation window testing as required by the study protocol, undergo randomization and blinding, and proceed with embryo transfer according to their assigned group.
Patients with unexplained recurrent implantation failure (RIF) meeting the diagnostic criteria for RIF: adult women under 40 years old who have failed to achieve clinical pregnancy after 3 embryo transfer cycles; or after transferring at least 3 high-quality embryos.
Female BMI: 18.5-25 kg/m².
Endometrial thickness ≥7 mm during the embryo transfer cycle.
Women planning to undergo frozen-thawed embryo transfer (FET) of blastocysts following in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).
Known causes of embryo implantation failure, such as infections, reproductive tract malformations, uterine cavity factors, adenomyosis or endometriosis, autoimmune system diseases (diagnosed by immunology department), hydrosalpinx, etc.
Couples with chromosomal abnormalities (excluding chromosomal polymorphisms) or familial genetic disorders in either or both partners.
Women with a history of recurrent miscarriage.
Women with contraindications to pregnancy or assisted reproductive technology.