Eggs, sperm & embryos
An expanded blastocyst has a large fluid-filled cavity that has stretched and thinned the zona pellucida, the shell around the embryo. Expansion is one of the features used in grading, and expanded blastocysts are commonly chosen for transfer or freezing.
Also known as: expanding blastocyst, grade 4 blastocyst
Related South Africa guides
Sources
- ESHRE/ICMART glossary and ESHRE laboratory guidance
Last reviewed: 8 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.