blastocyst
Pronunciation: BLAS-toh-sist
Advanced embryo stage with fluid-filled cavity, typically developing 5-6 days after fertilization.
Full Definition
A blastocyst is an embryo that has developed for approximately 5-6 days after fertilization and contains a fluid-filled cavity called the blastocoel. This developmental stage consists of two distinct cell types: the inner cell mass (which will become the fetus) and the trophectoderm (which will form the placenta). Blastocyst transfer is often preferred in assisted reproductive technology because embryos that reach this stage have demonstrated higher developmental potential and implantation rates compared to earlier-stage embryos. The blastocyst stage is also optimal for embryo biopsy procedures used in preimplantation genetic testing, as cells can be safely removed from the trophectoderm without affecting the inner cell mass.
Usage
Usage note: Specify day 5 or day 6 when relevant to indicate precise developmental timing.
In Context
- "The blastocyst demonstrated excellent morphology with a well-defined inner cell mass." — Embryology report
- "Blastocyst transfer resulted in higher implantation rates compared to day 3 transfers." — Research study