Impact of Sequential Double Embryo Transfer on Live Birth Rates: A Case-Control Study.

The main aim of this study is to evaluate the impact and identify potential indications for sequential double embryo transfer (SEQ-ET) in couples undergoing assisted reproductive technology (ART). The study will compare live birth rates (LBR) between patients receiving SEQ-ET and those receiving standard double embryo transfer (DET), while assessing safety outcomes and potential indications, including endometrial immune under-activation. Each SEQ-ET case will be matched with a DET control based on age, transfer attempt rank, and ART technique. We hypothesize that SEQ-ET may enhance implantation in couples with previous ART failures without increasing the risk of complications, potentially through localized maternal-endometrial immune communication initiated by the initially transferred cleavage-stage embryos.