Embryo, day three transfer versus Blastocyst, day five transfer
Transferring embryos at the blastocyst stage may be an option for patients in an IVF cycle. As background, a blastocyst is an embryo that has undergone multiple cellular divisions with the formation of a cavity within it. A fertilized egg reaches the blastocyst stage usually 4 to 5 days after fertilization. We encourage the majority of patients in my clinic to have their transfer earlier, on day 3, when the embryos have approximately 8 cells. For most patients, the best embryos are identifiable at this time and we like to transfer them into the uterus (their natural environment) as soon as possible. Embryos that are not transferred can be frozen for later use. However, if a patient has a large number of embryos and/or the best embryos are not clearly identifiable on day 3, we may suggest waiting 2 more days and doing a blastocyst stage transfer. Waiting gives us more information on how well the embryos are developing and may allow us to make a better choice for transfer. The downside of allowing embryos to grow to day 5 is that not all will develop to the blastocyst stage and therefore there may be fewer or no embryos to freeze after the transfer. In addition, blastocysts do not tolerate the freezing procedure as well as embryos frozen at earlier stages, so your chance of pregnancy with frozen embryos may be lower.
There are advantages and disadvantages to transferring embryos or blastocysts. You may discuss the options which best suit your case with your physician or the embryologist. Issues for you to consider are listed below.
If you have any questions about the Day 3 vs. Day 5 transfer, I’d love to hear from you.