Compaction and morula

Compaction is the process, usually seen around Day 4 of embryo development, in which the individual cells of the embryo begin to flatten and merge together rather than remaining as separate, distinct cells. Once compaction is complete, the embryo is described as a morula, a solid ball of cells, before it develops further into a blastocyst. Compaction and morula formation are expected steps on the way to the blastocyst stage; embryos that compact later than usual, or not at all, may still be assessed individually by the embryology team rather than being excluded automatically.

Also known as: morula, compacting embryo

Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.