Dr Smith :
The primary reason embryos do not make it to the blastocyst stage is because they do not possess the necessary genetic instructions for continued growth. No one can change or improve the genetics of an embryo. Assuming the lab is competent (and most are), there is no "risk" associated with continuing to culture the embryos to the blastocyst stage. I think you're making the false assumption that the embryos are better off in your uterus on day 3. They're not. Under natural conditions, the embryo remains in the Fallopian tube until the fifth day of development (blastocyst stage). The uterine environment on day 3 is not the same as the Fallopian tubes. When sequential culture systems are employed to grow the embryos to the blastocyst stage, the conditions in the laboratory more closely resemble the Fallopian tubes. Therefore, the embryos are better off in the lab for day 4-5 of development.
The point of growing embryos to the blastocyst stage in the laboratory is to deliberately weed out the embryos that do not have the genetic potential for continued growth. The "risk" you speak of doesn't really exist. If they're gonna make it, they do. If they don't, they don't. Of course, there's always the "risk" that no embryos make it to the blastocyst stage in the laboratory, but (because the problem is related to the genetics of the embryo, not culture conditions in the laboratory) they wouldn't have made in the uterus either.
I hope this clears things up. Good luck. I hope things work out for you.
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