Should You Transfer a Mosaic Embryo? What You Need to Know Before Deciding

If you’ve gone through IVF and had your embryos tested with preimplantation genetic testing (PGT-A), you may have encountered a term that left you feeling confused and uncertain: mosaic embryos. It’s not uncommon for patients to receive this result and immediately ask, What does this mean? Does this embryo still have a chance? Should I transfer it?

In the past, mosaic embryos were considered non-viable, meaning they weren’t thought to have the potential to result in a healthy pregnancy. But scientific research and clinical experience have changed our understanding of mosaicism. I’ve seen patients who had only mosaic embryos left go on to have healthy pregnancies and babies. I’ve also seen the emotional turmoil that comes with trying to decide whether to transfer a mosaic embryo, given the lingering uncertainty about its potential.

There is no one-size-fits-all answer to the question, “Should you transfer a mosaic embryo?” This decision is deeply personal and requires a clear understanding of what mosaic embryos are, the different types of mosaicism and their success rates, and the risks involved. In this article, I’ll break down the science, share my approach as a reproductive endocrinologist (REI), and offer guidance to help you navigate this difficult choice.

I’m Dr. Lucky Sekhon, a double-board certified REI practicing in New York. I use this blog, along with my Instagram account and monthly newsletter, to help educate and empower people to take control of their fertility with scientifically backed data and real clinical insights. If you’d like to stay informed, follow me on Instagram and subscribe to my monthly newsletter for the latest fertility updates.

What Are Mosaic Embryos?

Mosaic embryos are a unique category of embryos identified through preimplantation genetic testing (PGT-A), where some cells have the correct number of chromosomes (euploid), while others have an abnormal number (aneuploid). This happens due to errors in early cell division, leading to a mix of normal and abnormal cells within the same embryo. Unlike fully abnormal embryos, which typically fail to implant or result in miscarriage, some mosaic embryos have the potential to develop into healthy pregnancies.

There are different types of mosaicism, which can influence the chances of success. Segmental mosaicism occurs when an embryo has 46 chromosomes, but a small piece of one chromosome is missing or duplicated. Because the total chromosome count remains normal, segmental mosaics have the highest success rates among mosaic embryos. Whole chromosome mosaicism is when some cells have a full extra or missing chromosome (e.g., 47 or 45 chromosomes instead of 46), leading to moderate success rates and a higher risk of complications depending on which chromosome is affected. Complex mosaicism involves abnormalities across multiple chromosomes and has the lowest success rates due to widespread chromosomal errors.

Mosaic embryos are also classified as low mosaic or high mosaic based on the proportion of abnormal cells. Low-mosaic embryos (<50% abnormal cells) have higher implantation rates and are more likely to behave like normal embryos. High-mosaic embryos (50-80% abnormal cells) have a greater proportion of abnormal cells and are associated with lower implantation rates and a higher risk of miscarriage. Each type of mosaicism can exist in either a low- or high-mosaic state—for example, a low-mosaic segmental embryo has a high chance of success, while a high-mosaic complex embryo has the lowest chance of leading to a healthy pregnancy. Understanding these classifications helps fertility specialists guide patients on whether a mosaic embryo transfer is a viable option.

Can You Get Pregnant with a Mosaic Embryo?

Yes, you can get pregnant with a mosaic embryo, but the likelihood depends on multiple factors, including the type of mosaicism, the proportion of abnormal cells, and which chromosomes are affected. Over the years, research and clinical experience have shown that mosaic embryos can implant and lead to healthy pregnancies, upending long-held views within the reproductive community that treated mosaic embryos like they were aneuploidy, avoiding transfer of them completely.

However, recent studies have called this thinking into question, as they have shown that while the implantation and live birth rates of mosaic embryos are lower than the 60-70% expected of a euploid embryo, mosaic embryos do have reproductive potential depending on the type of and the degree of mosaicism. For instance, a recent study of 1,000 mosaic embryo transfers found that in cases of segmental mosaicism, where only part of a chromosome was missing or duplicated, the live birth hovered around 43%. Further, embryos classified with whole chromosome mosaicism (having 1 extra or less chromosome) showed live birth rates of 33-36%, while embryos exhibiting complex mosaicism had a lower live birth rate of ~20%. It’s also important to remember that the proportion of abnormal cells also has a big impact on live birth rates, with high mosaic embryos shown to have an average live birth rate of 19% versus a 36% live birth rate seen in low mosaic embryos.

Mosaicism Type	Live Birth Rate
Segmental	43.1%
Whole Chromosome	31.3%
Complex	20.8%

Should You Transfer a Mosaic Embryo?

If you’re here, reading this section, chances are you’ve been given a mosaic embryo result and are now facing an incredibly difficult decision—one you never expected to have to make. First, let me just say: I see you. I know the emotional weight this carries. I’ve had so many patients sit in front of me with tears in their eyes, asking, What does this mean? Is this embryo still a chance at a baby? Or is this just another heartbreak waiting to happen?

I wish I could give you a clear, one-size-fits-all answer, but the truth is that this is one of those nuanced areas of reproductive medicine where each case is unique. The decision to transfer a mosaic embryo is deeply personal, requiring a careful balance of science, clinical judgment, and personal comfort with uncertainty. While some mosaic embryos result in healthy, live births, others may fail to implant or end in miscarriage. That’s why it’s so important to truly understand the details of your specific embryo’s abnormalities, rather than just seeing the word “mosaic” as a blanket category.

How I Prioritize Mosaic Embryos for Transfer

In my clinical practice, I do have a preference and an algorithm I use when helping patients decide if, and when, to transfer a mosaic embryo. In general, here’s how I approach it:

• Segmental mosaics are my first choice – These embryos have a small missing or duplicated part of a chromosome, but they still have the correct total number of chromosomes (46). Research shows segmental mosaics have the highest live birth rates and behave more like euploid embryos.
• Whole chromosome mosaics come next – If the embryo has a full extra or missing chromosome in some of its cells, it’s more of a gray area. Some chromosomes are more compatible with life than others, and this is where detailed discussions with a genetics counselor are crucial.
• Complex mosaics are the last consideration – If an embryo has multiple chromosomes affected, the success rate drops significantly. These embryos have the lowest implantation rates and highest miscarriage risks. In these cases, I’m more likely to recommend another retrieval, if possible.

In addition to the type of mosaicism, I also look at how much of the embryo is affected:

• Low mosaic embryos (<50% abnormal cells) have much better chances of implantation and success, often behaving more like euploid embryos.
• High mosaic embryos (50-80% abnormal cells) carry a higher risk of miscarriage and implantation failure, and I tend to recommend them only when no better options exist.

What Else Should You Consider When Deciding?

Beyond factors relating to the type and degree of mosaicism, there are other important considerations to keep in mind when making the decision whether to transfer a mosaic embryo or not:

If you have euploid embryos, those are always the first choice for transfer. But if your only remaining embryos are mosaic, it might be worth seriously considering a mosaic transfer—especially if another retrieval isn’t an option or unlikely to succeed due to advanced age or diminished ovarian reserve.

There is also a financial consideration to keep in mind when faced with the decision of transferring a mosaic embryo versus attempting another egg retrieval cycle. Undergoing IVF is not cheap, and a recent study has shown that in women over the age of 42, the cost of an additional retrieval cycle with PGT, which can be almost $20,000, yielded only a 10.2% increased chance of liver birth than a mosaic embryo transfer.

Making the Best Choice for You

There are no easy answers when it comes to the decision on transferring a mosaic embryo. However, the biggest mistake you can make at this juncture is to assume that all mosaics are created equal. Some abnormalities are more concerning than others. This is where your REI and genetics counselor come in—they can walk you through the details of your specific embryo’s chromosomal makeup and help you understand what the risks really are. This isn’t a decision you should make alone.

At the end of the day, this isn’t just a clinical decision—it’s an emotional one too. It’s about science, but it’s also about hope, risk tolerance, and personal values. Some patients feel completely at peace transferring a mosaic embryo, knowing it may be their best shot at a baby. Others choose to pursue another retrieval or consider other options.

What I want you to know is that there is no wrong choice here. You are making the best decision you can with the information you have. If a mosaic embryo is your only option, I want you to feel hopeful—because I’ve seen them work. I’ve had patients go on to have perfectly healthy babies from embryos that were once considered “too risky.”

And if you decide that transferring a mosaic embryo isn’t right for you, that’s okay too. There are other options, and your journey isn’t over. So, ask the questions, talk to your doctor, get the genetic counseling, and take your time. No one can predict the future, but with the right information and support, you can make the decision that’s right for you.