Eggs, sperm & embryos
A morula is the stage around day 4 when the embryo's cells compact into a tight ball with the boundaries between them becoming indistinct. It marks the transition between the cleavage stage and blastocyst formation, and is a normal step rather than a problem.
Also known as: day 4 embryo, compaction
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.