Blue yellow and green mosaic tile patternWhat is a Mosaic Embryo?

A mosaic embryo is an embryo that has some chromosomally normal cells and some abnormal cells. It is highly contested whether a mosaic embryo is normal or abnormal, leaving both doctors and patients confused about what to do regarding this embryo type. Mosaic embryos are identified during a preimplantation genetic testing (PGT) test. A small biopsy from the embryo is tested to check if it is normal or abnormal, to determine if it should be implanted during the IVF process. So what happens when it is both?

Mosaic Embryos for Fertility

Mosaic embryos are something to be aware of when working with any patient undergoing fertility treatment. Although scientists have not been able to agree on whether or not this type of embryo is truly abnormal, here is what we do know about mosaic embryos and fertility

  1. There is very little data on what happens to embryos when they are put back into the uterus. Some doctors believe that even if an embryo has some abnormal cells, it may still be viable. 
  2. Mosaic embryos have a much lower pregnancy rate (30% vs 75% for normal embryos).
  3. Mosaic embryos have a higher miscarriage rate (15% or higher vs. 3% for normal embryos).
  4. There is very little data on what will happen to babies that are born healthy, and whether starting out as a mosaic embryo may lead to health risks for the child later in life. 


So, while there is not a huge amount of data to give a sure answer on what should be done with mosaic embryos, you should provide your patients with basic information so they can better understand the potential benefits and risks. Our patients look to us for answers to things they don’t understand, so it helps to provide as much information as we can.

What Your Patients Need to Know

If your patient’s embryo comes back from testing and is identified as a mosaic embryo, the next step is up to them. There are a few choices for your patients to be aware of. First, they may choose to transfer the mosaic embryo. This is sometimes the best decision for patients who have been unable to produce a normal embryo. I often suggest that patients consider going through another retrieval to attempt to make a normal embryo, or discuss other options with their doctor. This is a difficult decision to make due to our limited information about mosaic embryos, but it is ultimately the patient’s personal choice. 


Another option is to discard the embryo. Discarding the mosaic embryo is very understandable given the risk of miscarriage, birth defects, and other unknown factors. Inform your patient that their embryo can be donated to help further the research of mosaic embryos and help advance medicine and knowledge in this area.


Lastly, patients may choose to simply postpone any further use of the embryo. To postpone means to leave the mosaic embryo in storage (it will be frozen in a medical facility just like any other embryo) and wait to try and produce a normal embryo, saving the mosaic embryo as a backup. Some patients may want to freeze the mosaic embryo in case research advances as time passes.

At the End of the Day…

At the end of the day, your patients need to know that this is a deeply personal choice they will have to make. As their doctor, you can, of course, suggest what you believe the best course of action would be – perhaps they are good candidates for trying again to get a normal embryo. Or, maybe you know that this might be their best shot at achieving a pregnancy and a risk they are willing to take. As long as your patients understand the risks and unknowns of transferring a mosaic embryo, then it is in their hands to determine the next step in their fertility treatment process. 

What Questions Do You Have About Mosaic Embryos? 

Are you seeing more mosaic embryos among your patients as genetic testing advances? How are you helping your patients with mosaic embryos move forward and make a decision? I’d love to hear your thoughts and learn more about how your patients are choosing to move forward, and how you are guiding them along the way. Feel free to contact me or reach out via social media so we can discuss this topic and more.

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