Blastocyst Transfer: Process and Success Rates

With as many as 1 in 8 couples in the US struggling with infertility,1the numbers of couples who choose to start building their families through IVF is on the rise. Assisted reproductive technologies continue to develop, and one of the most promising new techniques is the Day 5 or blastocyst transfer – but does it really live up to the hype? Let’s go through what happens in a Day 5 transfer.

Blastocyst or embryo? What happens in a Day 5 transfer?

embryo development zygote blastocyst

In a standard IVF procedure, the eggs retrieved from the mother are fertilized in the lab and left to develop. After fertilization, they are called embryos. In most IVF procedures, these embryos are incubated in the lab for 3 days before being transferred through a catheter into the mother’s uterus, where one will hopefully implant.

However, after developing for 5 to 6 days, the embryo reaches a more complex stage of development made up of two cell types. In a natural conception, that’s usually the point reached by the time a fertilized egg completes its journey through the fallopian tubes and into the uterus. After this point, it’s called a blastocyst.

A blastocyst transfer means that the embryos are incubated in the lab until Day 5 or 6 after fertilization. This makes it easier for fertility specialists to “grade” the embryos, and see which one are likeliest to implant and begin a pregnancy.

Blastocyst transfer success rates

In Vitro Fertilization IVF

According to some study, transferring blastocysts seems to improve the chance of giving birth to a healthy baby, especially if the mom is under 35. However, whether or not a blastocyst “sticks” depends on a number of factors: the mother’s age, the number of eggs retrieved, the blastocyst quality, and the techniques used by the fertility clinic all play a role.

For patients who responded well to gonadotropin fertility drugs, implantation rates of blastocysts transfer can reach 50%, with pregnancy rates of as much as 66.3%.2However, fertility rates decline with age, so the younger you are when you start treatment, the more likely you are to get pregnant from a blastocyst transfer.

Blastocyst transfer pros and cons

pros and cons

The blastocyst stage is where an egg needs to get to the uterus in order to implant. Not every fertilized egg will make it to the blastocyst stage, so by waiting until Day 5, your fertility specialists will be able to identify the embryos that have the best chance of getting you pregnant. This allows them to transfer just one high-quality embryo at a time, decreasing the risk of a high-risk multiple birth.

Since a blastocyst arrives to implant in the uterus on around the 5th day of a natural conception, there could be a better synchronization between the blastocyst transferred on Day 5 and the uterine lining.

On the other hand, there’s unfortunately a chance that your embryos might not make it to the blastocyst stage in the lab. Even if there’s no guarantee that they would have developed any further in utero, some practitioners and patients prefer to at least give transfer a shot on Day 3, given that some “borderline” embryos do manage to result in a pregnancy.

Ask your fertility specialist about blastocyst transfer

doctor couple talk hospital clinic

Not every woman undergoing IVF chooses a Day 5 transfer, and plenty of moms do go on to have a healthy pregnancy with an embryo transfer on Day 3. However, waiting until the blastocyst stage in the lab does allow your fertility team to select the embryos with the best odds of implanting into the uterus, while at the same time reducing the odds of twins or triplets. If you’re considering starting a cycle of IVF, ask your fertility specialist if you’re a good candidate for Day 5 transfer.