Glossary · Definition · v2026.3
What Is a Blastocyst?
A blastocyst is an embryo that has developed for about five to six days after fertilization. At this stage the embryo forms a fluid-filled cavity and differentiates into two main cell groups: the inner cell mass, which can develop into the fetus, and the trophectoderm, which later contributes to the placenta.
Clinical significance
In IVF practice embryos that reach the blastocyst stage are often selected for transfer because embryologists can better observe development and implantation potential at this stage.
Common confusion
Many patients assume that reaching the blastocyst stage guarantees pregnancy. In reality, implantation depends on multiple biological factors beyond embryo development alone.
Related reference
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This content defines terminology for educational orientation. It does not constitute medical advice.
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