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

Embryo transfer is a critical step in the in vitro fertilization (IVF) process, where an embryo is placed into the uterus in hopes of achieving pregnancy. At the Fertility Institute of San Diego, led by our esteemed medical director, Dr. Minoos Hosseinzadeh, we strive to offer personalized care and the most advanced treatment options. One of the key decisions in the IVF process involves choosing between a Day 3 and a Day 5 embryo transfer. This decision can significantly impact the outcome of your treatment.

Understanding Embryo Development

Before delving into the differences between Day 3 and Day 5 transfers, it’s important to understand the stages of embryo development. After fertilization, the embryo begins a process of division:

Day 1: The embryo is at the zygote stage, consisting of a single cell.
Day 2-3:
The embryo divides to become a 4-8 cell embryo.
Day 5-6:
The embryo reaches the blastocyst stage, consisting of 70-100 cells.
These stages are crucial as they reflect the embryo’s ability to grow and develop into a healthy pregnancy.

Day 3 Embryo Transfer

A Day 3 embryo transfer involves transferring the embryos back into the uterus at the cleavage stage, when the embryo has about 4-8 cells. Dr. Hosseinzadeh explains, “Day 3 transfers are considered when there are concerns about the number of embryos reaching the blastocyst stage. It can be beneficial for patients with fewer embryos or for those whose embryos do not typically thrive in a laboratory setting.”

Advantages of Day 3 Transfer:

Higher number of embryos available: This can be a more suitable option for patients who do not have many embryos.
Less time in the lab: Reduces the exposure of embryos to the artificial conditions of the laboratory.


  • Lower implantation rates: Generally, Day 3 embryos have lower implantation rates compared to Day 5 embryos.
  • Harder to select the best embryo: At this stage, it is more challenging to discern the embryos with the best developmental potential.
  • Day 5 Embryo Transfer
  • A Day 5 transfer, or blastocyst transfer, is when the embryo is allowed to develop to the blastocyst stage before being transferred into the uterus. Dr. Hosseinzadeh notes, “Day 5 transfers have become increasingly popular due to higher implantation rates and better outcomes. This approach allows us to observe the embryos longer, selecting the ones with the best potential for successful pregnancy.”

Advantages of Day 5 Transfer:

  • Higher implantation rates: Blastocysts have a higher chance of implanting once transferred.
  • Better selection process: Allows for the natural selection of the most viable embryos.


  • Fewer embryos make it to transfer: Not all embryos will develop to the blastocyst stage, potentially leaving fewer options for transfer.
  • Making the Decision: Day 3 vs. Day 5
  • The choice between a Day 3 and a Day 5 embryo transfer is made based on several factors, including the number of available embryos, their quality, and the patient’s previous IVF history. Dr. Hosseinzadeh emphasizes, “Our approach is always personalized. We consider all factors, including the patient’s age, fertility history, and the embryo quality, to recommend the best day for transfer.”

Understanding the differences between Day 3 and Day 5 embryo transfers is vital for anyone undergoing IVF. Each option has its benefits and limitations, and the decision should be made in close consultation with your fertility specialist.

If you’re ready to start your fertility journey, please book a complimentary virtual consultation with Dr. Hosseinzadeh, to go over fertility options or any other reproductive healthcare questions, click here.

American Society for Reproductive Medicine – Embryo Transfer
Society for Assisted Reproductive Technology – Embryo Development
National Institutes of Health – Clinical Outcomes for Day 3 vs. Day 5 Transfer

Book Your Free Initial Video Consult

By submitting this form, you consent to receiving SMS and Email appointment reminders, marketing messages, general information, and healthcare-related messages from Fertility Institute San Diego, including those sent by autodialer. Message and data rates may apply. Message frequency varies. You can unsubscribe at any time by replying STOP or clicking the unsubscribe link in our messages. View our Privacy Policy and Terms of Service.

Popular Fertility Reads


More Fertility Reads

Fertility Clinic in San Diego

Have a question? Our fertility specialists are happy to assist




Pay Bill