Trophectoderm
Pronunciation: troh-FEK-toh-derm
The outer cellular layer of the blastocyst that will develop into the placenta and extraembryonic tissues.
Full Definition
The trophectoderm is the outer epithelial layer of the blastocyst that surrounds the inner cell mass and blastocoel cavity. During embryo grading, trophectoderm quality is assessed based on cell number, cohesion, and appearance, typically graded as A (many cells, tightly packed), B (few cells, loosely grouped), or C (very few large cells). This layer is crucial for implantation and will eventually form the placenta and fetal membranes. In preimplantation genetic testing, cells are biopsied from the trophectoderm rather than the inner cell mass to avoid damaging the future fetus.
Usage
Usage note: Often abbreviated as 'TE' in embryology reports and grading systems.
In Context
- "The blastocyst showed excellent trophectoderm quality with grade A cellular organization." — Embryology report
- "Trophectoderm biopsy was performed on day 5 for genetic testing." — Laboratory procedure note