The question of when an embryo is transferred is important to the infertile couple's IVF outcome. Typically, embryo transfer (ET) is performed around day three after fertilization. Embryos are considered to be at the blastocyst stage of development immediately prior to hatching, around five to six days after egg retrieval. There is increasing evidence that waiting until that stage of development to transfer results in higher implantation rates per embryo.
Reasons for the higher success rates include:
- It is easier to choose healthier embryos for transfer when they are farther along in development.
- Transferring to the uterus five to six days post-fertilization results in a uterine environment for the embryo that more closely resembles a healthy natural conception.
Also, patients who are also using preimplantation genetic diagnosis (PGD) will be using blastocyst transfer. Embryos that are biopsied in the PGD process are grown to the blastocyst stage.
When blastocyst transfer is the chosen procedure, the patient will first be scheduled for embryo transfer on the third day after egg retrieval. On that day, the IVF lab staff will evaluate the embryos and if there are at least five high-quality embryos, the transfer will be rescheduled for Day 5.
There is a risk that none of the embryos will develop to blastocyst stage. On average, about half of fertilized eggs achieve the blastocyst stage. When there are no embryos to transfer as of day six, the distressing news might be tempered with the knowledge that the non-developing embryos would likely not have resulted in pregnancy if they had been transferred earlier.
