Blastocyst Stage

By Day 5, a healthy embryo will be at the blastocyst stage, with at least 128 cells.

• In natural conception, the embryo normally reaches the uterus from the fallopian tube about 5 days after fertilization - when the embryo is at the blastocyst stage.
• Therefore, theoretically, embryo transfer at the blastocyst stage may result in a higher IVF success rate.

In general

• Good embryos which develop according to schedule and appear normal in appearance under the microscope, may be allowed to become blastocysts before transfer.
• If the embryos are of lesser quality, one must consider the advantage and the disadvantage of aiming for a blastocyst transfer anyway.
• Plus: It is a good sign of embryo quality if the embryo reaches blastocyst stage by Day 5.
• Minus: Embryos that do not progress to blastocyst or even to morula stage by Day 5 may have benefited from a Day-3 transfer. The uterus is still the best incubator for embryos
because it produces natural nutrients for the embryo.

In donor egg IVF, embryo transfer is generally done on Day-5, because a young donor with healthy eggs is likely to produce good-quality embryos that will benefit from being transferred at the blastocyst stage.

Two other decisions must be made with the couple about embryo transfers:

• How many embryos to place into the uterus?
• Whether to do assisted hatching?

Both depend on embryo quality primarily.

These considerations will be discussed with the couple by Dr. Brandeis before proceeding to the transfer.