When will my embryo transfer happen?

We are focused on maximising your chances of pregnancy. One of the most important influences to consider is the day embryo transfer should take place. At your planning session, this will most certainly be discussed but the final decision may not actually be made until the potential day of your transfer.

The day of the embryo transfer is typically decided by the embryology team. They will evaluate the quality of your embryos, the number available and your background (including maternal age, previous treatments, medical history, etc.) among other relevant information. Together you will discuss your wishes and decide the best day to transfer the embryos back into the uterus.

Usually, the procedure is performed on day 2, day 3 or day 5 of the embryo development but occasionally, due to certain cycle requirements, it might be performed on day 4 or day 6. For example, fresh embryo transfers for women undergoing pre-implantation genetic testing for aneuploidies, or for single gene disorders, may be performed on day 6 - but some units now freeze all the embryos and replace in future cycles.

There are important differences to highlight between transferring an embryo at the cleavage stage (day 2 to 3) or when they become blastocysts at day 5 and day 6. It is essential to understand what difference this makes to the rate of success. Generally speaking, there is a higher likelihood to have an actual transfer if the choice is to transfer on day 2 or 3. The reason behind this phenomenon is that not all the embryos are capable of reaching day 5 and becoming a blastocyst - which in some occasions could lead to transfer cancellation. On the other hand, as culturing embryos up to day 5 could be considered a selection method (only the strongest embryos will reach the blastocyst stage), the transfer of blastocysts would provide a higher pregnancy rate.

Typically, with blastulation rates above 50% (that’s the percentage of the fertilised eggs that might become blastocysts), the transfer of embryos on day 5 would be ideal for those patients that have one, two or more embryos than the desired number to be used for embryo transfer. Still, the decision between early or late transfer should be made on a daily basis as human embryos are dynamic structures and quality might fluctuate over time.