Blastocyst
embryologyDefinition
A Day 5-7 embryo with a fluid-filled cavity, an inner cell mass, and a trophectoderm layer.
In IVF Treatment
Blastocyst culture gives the lab more development information before transfer or freezing. Embryos that reach blastocyst stage may have stronger transfer potential in some contexts, but clinic guidance depends on the full treatment picture. Grading (e.g., 4AA, 5BB) helps inform embryo selection.
Frequently Asked Questions
What does a 5AA blastocyst mean?
The number indicates blastocyst expansion. The first letter grades inner cell mass appearance, and the second letter grades trophectoderm appearance. A 5AA is a highly expanded blastocyst with high appearance grades, but it cannot determine an individual outcome.
Is a blastocyst better than a Day 3 embryo for transfer?
Blastocyst transfer can be useful in some situations, but not all embryos reach blastocyst stage and not every patient benefits from extended culture. Your embryologist will recommend the approach based on your specific embryo development.