Embryonic factors affecting outcome from single cryopreserved embryo transfer.

Area of Science:

• Reproductive Medicine
• Embryology
• Assisted Reproductive Technology

Background:

• Single embryo transfer (SET) is increasingly used to minimize multiple pregnancies.
• SET with cryopreserved embryos is less common than with fresh embryos.
• Understanding criteria for successful SET with cryopreserved embryos is crucial.

Purpose of the Study:

• To define embryonic characteristics for successful single cryopreserved embryo transfer (SCET).
• To identify criteria for SCET achieving success rates comparable to double cryopreserved embryo transfer (DCET).

Main Methods:

• Retrospective analysis of 6916 cryopreserved day-2 embryo transfer procedures.
• Comparison of clinical pregnancy and implantation rates between SCET and DCET.
• Evaluation of embryonic characteristics, including cryopreservation stage, blastomere loss, and post-thaw cleavage.

Main Results:

• DCET yielded higher clinical pregnancy rates but also higher multiple pregnancy rates (26.7% in women <36).
• Optimal SCET in women <36 (30.9% implantation rate) associated with cryopreservation at 4-cell stage, <2 blastomere loss, and ≥2 surviving blastomeres.
• In 4-cell stage embryos, single blastomere loss did not impact implantation; single post-thaw blastomere did not increase implantation potential.

Conclusions:

• Specific embryonic criteria can guide successful SCET.
• These thresholds provide a rational basis for selecting embryos for SCET.
• SCET can achieve comparable success to DCET while reducing multiple pregnancy risks.