In Vitro Fertilization (IVF)

Blast Transfers

Day 3 versus Day 5 (“Blast”) Transfers

Traditionally during the in vitro fertilization process, embryos were transferred to a woman’s uterus three days after the eggs were retrieved. Recent advances in the culture media in which embryos grow have allowed the extended growth of embryos to day five, or the blastocyst stage. These blast transfers have advantages and disadvantages.

Potential advantages of blast transfers include:

Transfer occurs closer to the natural time an embryo enters the uterus when the uterine lining may provide a better environment for the embryo.
Allowing embryos to develop in the laboratory for a longer period of time allows for selection of the hardier embryos that are more likely to survive.
Because of this selection, fewer embryos can be transferred which allows for a reduction in the risk of multiple pregnancies (twins, triplets).

Potential disadvantages include:

The main risk for blast transfer is that some embryos will die in the laboratory. While we think these embryos have reduced potential, some may have survived if transferred at an earlier stage.
There is a risk that no embryos will survive to day five, so there may be no embryos for transfer.
There may be fewer embryos for freezing and subsequent cryopreservation cycles.

At Froedtert & The Medical College of Wisconsin’s Reproductive Medicine Center, we look at individual cases and offer blastocyst transfer to patients with a large number of quality embryos to try to avoid having a situation where no transfer occurs due to the loss of all embryos. Patients undergoing preimplantation genetic diagnosis (PGD) also have blast transfers due to the fact that the embryo biopsies occur on day three and the processing takes two days.