IVF & Fertility
Feb 5, 2026
1 min read
Blastocyst Culture: The 5-Day Embryo Selection Journey
Tracking the growth of embryos to Day 5, allowing for selection of high-grade blastocysts to optimize pregnancy rates.
Cleavage to Morula Stage
Following fertilization, the zygote begins to divide. On Day 2, it reaches the 2 to 4-cell stage, and by Day 3, it should be an 8-cell cleavage embryo. By Day 4, cells undergo compaction to form a morula. Culturing cells to Day 5 allows embryologists to evaluate which embryos have the highest developmental potential.
The Blastocyst Stage
On Day 5, the embryo forms a fluid-filled cavity, differentiating into the trophectoderm (which becomes the placenta) and the inner cell mass (which becomes the fetus). Selecting high-grade blastocysts for transfer significantly increases implantation rates and reduces the risk of multiple pregnancies.
🧠 Key Takeaways
- ✅ Day 3 cleavage embryos should display symmetric division.
- ✅ Morula compaction occurs on Day 4.
- ✅ Day 5 blastocysts show defined differentiation.
- ✅ Selecting blastocysts improves implantation rates.
