Usually, embryo transfer is performed on the third day after egg collection, when the embryo reaches the 6-8 cell stage. The decision to transfer embryos at the blastocyst stage (fifth or sixth day after egg collection) may increase success rates but requires special laboratory conditions. It is indicated in the following cases:
- When previous attempts of day 3 embryo transfer have inexplicably failed,
- When there is an excess of day 3 embryos with good embryo score. In cases like this, the embryo transfer is delayed and carried out at the blastocyst stage, enabling this way the embryologists to choose the most competent ones for transfer.
- When performing preimplantation diagnosis. In such cases, the embryo is biopsied on day 3 or 5 of culture and the embryo transfer is either necessarily performed on day 5 or 6, or in some cases all the embryos are frozen and the embryo transfer takes place in the next cycle (until the geneticists share the PGD results).
