Inner cell mass (ICM)

The inner cell mass is the tightly grouped cells inside a blastocyst that go on to form the fetus. Embryologists grade it by how many cells it contains and how well they are grouped, and it forms the first letter or number in most blastocyst grades.

Also known as: ICM

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.