Blastocyst
embryologyDefinition
A Day 5-7 embryo consisting of 100-200 cells organized into an inner cell mass (future baby) and an outer trophectoderm (future placenta), surrounding a fluid-filled cavity.
In IVF Treatment
Blastocyst culture allows natural selection to occur in the lab before transfer. Embryos that reach blastocyst stage have a higher implantation potential. Grading (e.g., 4AA, 5BB) helps select the best embryo for transfer.
Frequently Asked Questions
What does a 5AA blastocyst mean?
The number (3-6) indicates blastocyst expansion. The first letter grades the inner cell mass (A=good, B=fair, C=poor). The second letter grades the trophectoderm. A 5AA is a fully expanded blastocyst with excellent grades in both categories.
Is a blastocyst better than a Day 3 embryo for transfer?
Blastocysts generally have higher implantation rates per transfer due to natural selection. However, not all embryos reach blastocyst stage. Your embryologist will recommend the best approach based on your specific embryo development.