What is Blastocyst Transfer in IVF

In Vitro Fertilization, IVF involves stimulating the ovaries to produce multiple eggs, retrieving the eggs, exposing them to sperm causing fertilization, embryo incubation, and embryo transfer. Traditionally, embryos were transferred to the uterus after two to three days of incubation. A blastocyst is an embryo that has been cultured (usually 5-6 days) until it has differentiated into two distinct cell types. The outer cells are known as the trophectoderm, which will become the placenta, and the inner cell mass becomes the fetus.

As embryos develop, those less capable of survival do not continue to mature to the blastocyst stage. Blastocysts are “heartier” than day three embryos and produce higher implantation rates (the percentage chance that an embryo will initiate a pregnancy). Only, perhaps, 40% of the eggs that fertilize and form an early pre-embryo will develop to the blastocyst stage due to the limited developmental potential of most fertilized eggs. A major advantage of blastocyst transfer is that fewer embryos need to be transferred to the uterus, usually one or two blastocysts, thus dramatically lowering the rate of higher order (>3) multiple births. The actual number transferred is carefully determined for each couple and depends on the age of the mother and the appearance of embryo.

Blastocyst transfer cannot be used in all couples IVF cycles. There must be enough embryos surviving at day three to attempt to culture to the blastocyst stage. Blastocyst transfer is used as a selection technique to choose which embryos to put back when there are a large number of embryos to choose from. An embryo that will start a pregnancy at the blastocyst stage on day 5 would have started a pregnancy on day three at the cleaving stage. Some embryos are lost as the culturing process proceeds and if a couple only has two embryos at day 3 it is possible that none will survive to the blastocyst stage thus “losing” the treatment cycle. In these cases, transfer occurs on day 3. Again, blastocyst transfer is used to help select the embryos to be put into the uterus. If there are no embryos to select from, it is considered better to get the embryos back to the more normal environment of the uterus at an earlier stage.

Blastocyst transfer is used when possible and you should discuss the procedure with your fertility specialist