How Do Fertility Specialists Choose the Best Embryo for Transfer (and Could AI Help)?

May 31

Reviewed by Lina Akopians, MD, PhD, FACOG

During IVF, you may end up with more than one viable embryo. This is great news, but it opens up a question:

Which one should you and your doctor choose to transfer?

Doctors have access to more information today than ever before when making this important decision.

Learn about the embryo selection methods that fertility specialists use to help give patients the best chance of pregnancy.

How Doctors Used to Choose Embryos for Transfer

When IVF first became available, embryos were evaluated solely based on their morphology: how they looked under a microscope. Embryologists evaluated each embryo’s stage of development, cell count, and cell appearance, then assigned each one a grade, such as 4AA or 4BB.

Grading doesn't tell doctors everything about an embryo, but the information it provides is valuable. Research has shown a strong association between embryo grade and the potential for implantation.

Morphology is still an important part of IVF today. But now, fertility specialists layer on additional types of information to make even more informed decisions during IVF.

How Most Clinics Choose Embryos Today

Today, fertility clinics use a combination of morphology and genetic testing when selecting an embryo for transfer. Genetic testing identifies certain genetic abnormalities that could affect an embryo's chances of implanting and developing into a healthy pregnancy.

Using these methods together gives doctors more information than morphology alone. For example, two embryos may receive the same grade, but only one might have chromosomal abnormalities. That’s a key differentiating factor that can help determine which embryo to transfer.

Morphokinetics: A New Approach

As IVF continues to advance, researchers are exploring new ways to learn more about embryo quality. One growing practice is morphokinetics, which uses time-lapse imaging to evaluate embryo development.

Traditionally, embryologists check the embryos at a few select stages of development:

Day 1 (fertilization)
Day 3 (cleavage stage)
Days 5-7 (blastocyst stage)

While it’s helpful to know how the embryos look at each stage, some researchers believe that even more can be learned by watching how they develop. Time-lapse incubators take thousands of images across the development period, creating a video. Rather than seeing a few snapshots, embryologists can watch what happens between each stage and look for abnormalities such as errors in cell division.

One study found that embryos cultured using time-lapse technology had statistically higher pregnancy rates than those cultured using traditional incubation, but more research is needed to validate this finding.

AI in embryo selection

Some centers are taking time-lapse technology one step further by combining it with artificial intelligence (AI). New AI tools for IVF can analyze the time-lapse images, compare them to a dataset, and identify developmental abnormalities faster, and potentially with greater accuracy.

Because embryo grading involves interpreting images, it is inherently subjective. Even experienced embryologists can assign different grades to the same embryo. One study found only fair to moderate agreement between embryologists. AI may help make grading more consistent.

Importantly, AI is meant to support embryologists, not replace them. The embryologist still reviews the videos and makes the final recommendation, overriding AI when needed.
For patients, the most exciting parts of AI in IVF is being able to see their embryos develop.

Some time-lapse systems let patients watch videos of their embryos through an app, which can make an otherwise long wait between egg retrieval and embryo transfer feel a little easier.

What to Ask Your Doctor About Embryo Selection and AI in IVF

Different IVF clinics use different approaches in embryo selection. Time-lapse imaging and AI are still new advancements, and access to this technology is still expanding

When you're choosing a fertility clinic or discussing your IVF treatment plan, ask your doctor:

How do you decide which embryo to transfer?
Do you use genetic testing, and when do you recommend it?
Do you use time-lapse incubators or AI?
If you use AI, what is your center’s policy on how the final decision is made?

Choosing an embryo for transfer is one of the most important decisions in the IVF process. Don't hesitate to ask your doctor how they select embryos and why they recommend one embryo over another.