OP goes into this some, but US IVF typically does not. As I understand it, embryos are visually checked for gross chromosomal abnormalities like having too many

OP goes into this some, but US IVF typically does not. As I understand it, embryos are visually checked for gross chromosomal abnormalities like having too many chromosomes, and during pregnancy Down tests are often done, but PGD is typically not done unless there is a family history or some other reason of concern, and when PGD is done, it's usually (currently) limited to a small panel of well-known genetic diseases.