The optimal number of embryo cells for effective pregnancy and decrease of multiple pregnancy rate in frozen-thawed...

Area of Science:

• Reproductive Medicine
• Embryology
• In Vitro Fertilization

Background:

• Frozen-thawed embryo transfer (FET) is a key component of assisted reproductive technology.
• Optimizing FET protocols is crucial for improving pregnancy rates and reducing multiple gestations.
• The number of cells in an embryo at transfer may influence clinical outcomes.

Purpose of the Study:

• To investigate the effect of pre-frozen embryo cell number on clinical outcomes of day 3 double FET.
• To explore optimal embryo selection strategies for reducing multiple pregnancy rates.

Main Methods:

• Retrospective analysis of 2184 day 3 vitrified double FET cycles.
• Patients were grouped based on the number of cells in each of the two transferred embryos (e.g., 8-cell, <8-cell, >8-cell).
• Classification decision tree analysis was used to determine optimal transfer strategies.

Main Results:

• The 8-cell embryo groups (8C2 and 8C1->8C1) showed higher pregnancy and multiple pregnancy rates.
• The <8-cell embryo group (8C1-<8C1) had significantly lower implantation and multiple pregnancy rates.
• Optimized single embryo transfer (SET) strategies based on age and embryo cell number reduced multiple pregnancy rates from 38.5% to 16.9%.

Conclusions:

• The number of cells in pre-frozen embryos is a significant factor influencing FET clinical outcomes.
• Patient age, embryo cell number, and transfer history are valuable predictors for optimizing FET.
• Tailored SET strategies, prioritizing embryos with ≥8 cells for younger women and those in the first transfer, can improve reproductive efficiency and safety.