Embryo Grading
Three key indicators of blastocyst quality: embryo development stage + trophectoderm (TE) grading + inner cell mass (ICM) grading
Some embryos develop slowly and only reach the blastocyst stage on Day 6 (D6) or Day 7 (D7). Therefore, the day on which the blastocyst forms has also become an important factor in evaluating its future developmental potential.
Number: Embryo Development Stage (Six Stages)
The expansion and hatching level of the blastocyst cavity. If the embryo has reached stage 3–6, the ICM and TE morphology must also be assessed to complete grading.
Q&A
Q1
Should we transfer Day 3 (D3) or Day 5 (D5) embryos?
Transferring D5 embryos generally results in higher pregnancy rates. The extended culture period acts as a natural selection process—only stronger embryos that reach D5 are chosen, increasing the chance of implantation.
Q2
Can D3 embryos undergo genetic testing (PGS/PGD)?
Not recommended. D3 embryos consist of only 6–8 cells. When biopsied:
If only one cell is removed and it’s abnormal while the others are normal, it may lead to a misdiagnosis.
Removing two or more cells could compromise embryo development due to reduced cell count.
D5 blastocyst biopsy samples the outer TE cells, which are more numerous. Removing 3–5 cells has less impact and a lower misdiagnosis rate than D3 biopsies.
Q3
Why only transfer embryos on Day 3 or Day 5? What about Day 4?
While Day 4 embryos can be transferred, their morphology is typically unclear and harder to evaluate, so Day 4 transfers are uncommon.
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