Difference between a 3-day and a 5-day embryo transfer

When the fertilised embryos reach a certain stage of development, they are transferred into the woman’s uterus. If everything goes right, the embryo implants itself and this results in pregnancy. Embryo transfer can be done either on the 3rd or the 5th day of growth.

On day 3, the embryos will have four to eight cells. On day 5, the embryo will contain 70 to 100 cells and is called a blastocyst. The blastocyst has two types of cell. One kind will go on to form the baby and the other will become the placenta. It is only around one-third of embryos that will ever become a blastocyst.

The quantity of the embryos is what determines the day on which the transfer is made. On the third day, the doctors are already able to see which of the embryos are ideal and has a chance of growing into a baby. If the doctors can distinguish the ideal embryos from the others, the transfer is done on the third day. The environment in the uterus will further encourage the growth of the embryo and will make it more possible that the embryo grows to the blastocyst stage and implant itself.

If multiple embryos have been fertilised and all of them are growing in a fashion that makes it hard to distinguish the ones that are of the highest quality, doctors may ask you to wait until the 5th day before transfer. This is because the additional days will help them evaluate and decide which embryo has the best chance of going on to create a successful pregnancy.