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.

Inclusion Criteria:

• Infertile patients undergoing IVF with planned SEQ-ET or DET.
• Age ≤ 42 years.

Exclusion Criteria:

• Age aged 43 years.
• Cycles in which only a single embryo was ultimately transferred and cycles in which no embryo transfer occurred.

The study population consists of couples undergoing assisted reproductive technology (ART) at Pierre Rouquès - Les Bluets Hospital between January 2014 and December 2023. Female participants are biologically capable of becoming pregnant and have undergone either sequential double embryo transfer (SEQ-ET) or standard double embryo transfer (DET). The population includes women with a history of previous ART attempts, and does not exclude participants based on the presence or absence of a specific disease or condition.