Blastocyst
An embryo that has developed for about five to six days and formed a fluid-filled cavity with two distinct cell groups.
In plain English
It's an embryo that has grown for five or six days in the lab, reaching a more advanced stage than a day 3 embryo.
Why it matters
Blastocyst-stage embryos allow embryologists to select embryos with better developmental potential before transfer or freezing.
Related terms
Guides that cover this
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