Glossary · Definition · v2026.3
Frozen Embryo Transfer (FET)
A frozen embryo transfer uses a previously cryopreserved embryo, performed in a subsequent cycle with controlled endometrial preparation. FET is the dominant transfer modality in modern IVF practice.
How FET Cycles Work
FET cycles involve preparing the endometrium with estrogen and progesterone to create an optimal implantation environment. Transfer occurs when the lining reaches appropriate thickness (typically 7 mm or more). FET allows time for genetic testing results, avoids OHSS risk from fresh transfer, and enables elective single embryo transfer planning.
Biological Constraints
Vitrification survival rates exceed 95 percent for blastocysts. FET outcomes are comparable to or slightly better than fresh transfer outcomes in most populations. The main constraint is the additional time and cost of a separate cycle. Endometrial preparation may use natural cycle monitoring or hormone replacement protocols.
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This content defines terminology for educational orientation. It does not constitute medical advice.
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