D3 vs. D5 Embryo Transfer

Many patients often wonder whether it is better to have a Day 3 or Day 5 embryo transfer. At San Diego Fertility Center, we allow the embryos to guide us in determining which transfer day will give you the best chances of success in your IVF cycle. Embryo transfers can take place between Day 2 and Day 6 of embryo culture, but are most often performed on Day 3 or Day 5 when their stage of development is most clearly defined. Although there are benefits to having a transfer on one day or another, pregnancy rates are comparable whether the embryo transfer takes place on either day. The day of your embryo transfer is usually decided on Day 2 after the embryos have gone through one division and are somewhere between 2-4 cells. It is at this point that we begin grading the embryos.

On Day 3, an embryo should consist of 4-8 cells and is considered a multicell embryo. At this stage, embryos are graded based on stage of development (cell number), cell symmetry, and percent fragmentation. With a limited number of embryos, embryologists can more easily determine which embryos will yield the highest chance of pregnancy, based on the morphological grading. As such, a Day 3 embryo transfer is often recommended. The most beneficial reason for performing a Day 3 transfer is to return the embryo to its natural environment. Although the laboratory has proven success in blastocyst culture, the best incubator for embryos remains to be your uterus. When there are a large number of embryos, culturing to Day 5 allows us to distinguish which embryos have a greater potential for success. These same embryos may have looked very similar on Day 3. By Day 5, an embryo should consist of 64-128 cells and has reached a more advanced stage called a blastocyst. The cells of a blastocyst embryo are differentiated into two types: trophectoderm and inner cell mass. As the embryo grows, these two cell types eventually form the placenta and fetus, respectively. Embryos that reach the blastocyst stage have a higher chance of implantation (attaching to the uterine wall), resulting in fewer embryos transferred.

There are many factors that influence the day of your embryo transfer, including: quality of embryos, quantity of embryos, risk of multiples, and past IVF cycle history. You will receive daily updates regarding the development and grading of your embryos as well as recommendations that arise from our daily Patient Care Conference (PCC) with your physician, nurses, and embryologist. Together with you, it is our goal to make decisions to achieve the most successful outcome for your cycle.