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When an embryo has been cultured for five days (as 70 percent of our embryos are), it reaches what we call the "blastocyst" stage. The process of embryo transfer on Day 5 is called "blastocyst culturing" and it offers the advantage of what we refer to as "embryo selection."
The implantation rate of blastocyst transfer is greater than a transfer of Day 2 or 3 embryos. But only 20 to 50 percent of Day 2 embryos can develop in vitro to Day 5, no matter how perfect the in vitro culture system. In culturing until the blastocyst stage, then, there is a potential loss of what could have been viable embryos if implanted earlier, but those that make it to the blastocyst stage have a greater chance of making it to live birth.
Embryo selection has nothing to do with selecting embryos to produce babies with specific traits, but rather refers to the process of implanting older, more viable embryos - those that have been "selected" by their ability to survive in vitro to the blastocyst stage.
While most of our embryos are cultured to Day 5, and, therefore, do undergo blastocyst culturing and embryo selection, the decision of how long to culture embryos is based on the recommendation of your doctor while taking into account your clinical history.
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