Failure to detect on the eighth day of frozen embryo transfer is not necessarily a failure, but may be caused by the early testing time.
The embryos transferred are divided into cleavage embryos and blastocysts, for the cleavage embryos are generally mostly embryos formed by fertilized eggs cultured for about three days, and in most cases the pregnancy cannot be detected on the eighth day after the transfer. For blastocysts, which are embryos that are cultured for about five days from a fertilized egg, in most cases pregnancy can be determined eight days after the transfer by taking a blood test for human chorionic gonadotropin.
So there is variability in when the embryos are transferred and when they can be tested. Therefore not testing on the eighth day after transfer does not necessarily mean that the transfer has failed.
If you don’t get a test on the eighth day after transferring frozen embryos, it is recommended that you use a pregnancy test a week later or go to the hospital for a blood test for human chorionic gonadotropin to determine whether the transfer has been successful or not!