Why would a embryo transfer of a excellent quality blastocyst fail to implant? what should i ask at follow up?

Possible reasons ...: Could be - 1) genetic or metabolic abnormalities in the embryo, 2) problems with the lining of your uterus including polyps, or 3) difficulties with the embryo transfer itself. For 2) you should have had a saline sonogram (shg) or other procedure to check your cavity and ultrasounds to check your lining. Single embryo transfer (set) has a lower pregnancy rate than 2 embryos, even if you're young.