What Is a Blastocyst (Day 5 Embryo)?

A blastocyst is the advanced embryo stage reached on the 5th–6th day after fertilisation. Embryos that reach this stage have differentiated into the inner cell mass (which will form the baby) and the trophectoderm (which will form the placenta).

Because only embryos with high developmental potential can reach the blastocyst stage, blastocyst transfer provides a natural selection advantage and generally offers higher implantation rates. The readiness of the uterine lining on transfer day is also better aligned with the natural cycle on day 5.

At Clavis IVF Center, embryos are cultured in MINC+ incubators and monitored continuously with embryoscopy up to the blastocyst stage; the healthiest embryo for transfer is selected with AI-assisted analysis.

Key Points

• The day 5–6 stage after fertilisation
• Offers a higher chance of implantation
• PGT (genetic testing) is performed at this stage
• Monitored continuously with embryoscopy