inner cell mass
Also written as: ICM — inner cell mass
Group of cells within a blastocyst that develops into the fetus, as opposed to the trophectoderm which becomes the placenta.
Full Definition
The inner cell mass (ICM) is a cluster of cells located within the blastocyst cavity that gives rise to the actual fetus during embryonic development. In contrast to the trophectoderm cells that form the placenta, the ICM contains the pluripotent cells that will differentiate into all fetal tissues. In reproductive genetics, the distinction between ICM and trophectoderm is crucial because genetic testing typically samples trophectoderm cells, which may not always reflect the genetic status of the ICM due to potential mosaicism. The quality and size of the ICM is also an important factor in embryo grading and selection for transfer.
Usage
Usage note: Commonly abbreviated as ICM in embryology reports.
In Context
- "Embryo grading assessed both trophectoderm quality and inner cell mass development before transfer." — IVF laboratory report
- "The possibility of ICM-trophectoderm mosaicism was discussed when explaining potential limitations of PGT-A results." — Pre-procedure counseling note