What is the Difference Between a Day 3 and Day 5 Embryo Transfer?

When it comes to deciding between a Day 3 or Day 5 embryo transfer during In Vitro Fertilization (IVF), understanding the development of an embryo is essential. Let’s take a closer look at how an embryo grows and why doctors might choose one transfer day over the other.

The Development of an Embryo

An embryo begins as a single cell, dividing every 12-24 hours. By Day 3, the embryo consists of about 4-8 cells and is referred to as a multicell embryo. At this stage, all the energy and nutrients for cell division come from the mother’s egg.

By Day 5, the embryo has developed into a blastocyst, containing around 70-100 cells. A blastocyst has differentiated into two types of cells:

• Inner cell mass, which will develop into the fetus.
• Trophoblast, which will become part of the placenta.

At this point, the embryo activates its own genes through a process called genomic activation, allowing it to produce the energy needed for further cell division and growth. However, not all embryos reach the blastocyst stage—only about one-third of embryos successfully activate their genes and grow into blastocysts, making this development stage crucial.

Choosing Between Day 3 and Day 5 Transfers

At San Diego Fertility Center (SDFC), Dr. Hummel, Dr. Kettel, and the embryologists focus on selecting the “best” embryos for transfer, although what constitutes "best" can vary from patient to patient.

Day 3 Transfer

In cases where there is a smaller number of dividing embryos, the "best" embryos may be evident after just a few days in the lab. In these situations, a Day 3 transfer is often recommended. Transferring the embryos earlier allows the uterine environment to potentially support further embryo growth, blastocyst development, and successful implantation.

Day 5 Transfer

When there is a larger number of embryos, they may appear similar in quality after three days, making it harder to determine which ones are most likely to succeed. By waiting until Day 5, the embryos that are capable of forming blastocysts have sorted themselves out, allowing the doctors to transfer the embryos that have demonstrated successful development into the blastocyst stage. 

A Day 5 transfer ensures that the embryos selected for transfer have already achieved this critical milestone, which is a significant indicator of their potential for implantation.

Matching Individual Needs

The decision between a Day 3 or Day 5 embryo transfer is based on the number and quality of embryos, as well as each individual patient’s situation. Whether transferring on Day 3 or Day 5, the ultimate goal is to select the embryos with the best chances of success.

At San Diego Fertility Center, we carefully evaluate each patient’s unique case to determine the most appropriate transfer day, ensuring the highest chance for a successful pregnancy.

For more information on embryo transfer options and IVF, please contact San Diego Fertility Center. We are here to guide you through your fertility journey with expert care and personalized treatment plans.