What is up with mosaic embryos? Why is everyone in reproductive medicine talking about these things? What are they? Why should I care?
Mosaic Embryos are embryos that have some chromosomally normal cells and some chromosomally abnormal cells. If you are using IVF with PGS (Preimplantation Genetic Screening) to conceive or to avoid miscarriage or to avoid transmitting a genetic disease then you need to know about mosaic embryos.
PGS is the process of taking a cell or cells from an early stage embryo before it is implanted in the uterus in order to analyze the chromosomes in the embryo. If the cells are used to look for specific disease causing mutations like sickle cell disease or muscular dystrophy that is a related process called PGD or Preimplantation Genetic Diagnosis.
The PGS technique has now advanced to the stage of becoming so detailed that it can detect abnormalities that we have not detected before and have not studied before and therefore are not sure of their meaning. Mosaic Embryos can be detected now with the latest genetic analysis technique commonly called NGS or Next Generation Sequencing.
The problem is when an embryo is mosaic, scientists cannot know or agree if that embryo is truly abnormal or not. A mosaic embryo has some normal and some abnormal cells. There is very little data on what happens to these embryos when they are put back in the uterus. They seem to have a much lower pregnancy rate (30% vs 75% for normal embryos) and a much higher miscarriage rate (15+% vs 3% for normal embryos). There is no long term data because this technique is so new. What will happen with these pregnancies? The few babies that have been born appear to be normal but what will happen as they get older? Does starting out life as a mosaic embryo increase your health risks in the future? Will you still be normal and healthy at age 5, 10, 20, 40 years of age?
It is very possible that mosaicism at the early embryo stage can be perfectly normal but no one knows at this time.
So at this point, if you have a mosaic embryo in the freezer, it is important for you to decide what to do with your embryo.
Right now there are 3 options:
3) Postpone the decision
The first option: TRANSFER seems reasonable to consider if you do not have any completely normal embryos for transfer, or it is difficult for you to make completely normal embryos for transfer. This is a decision that should be discussed directly with your doctor because each person’s situation is different and this is often a very personal decision with no medical standards at this time. We do feel that given higher rates of birth defects and miscarriages in the short term compared to embryos that test normal (embryos that test normal still have a small risk for miscarriage and birth defects because we cannot test for everything) that if you do not have a normal embryo for transfer you consider going through another retrieval to make a normal embryo or discuss other options with your IRMS doctor. Another concern is the complete lack of any long term safety data. Ultimately this is your decision and there are no wrong answers but it is important to discuss all your questions with your doctor so you make the right decision for you given the information that we have.
The second option: DISCARD, is very reasonable because of the concerns above. If you decide to discard your embryos, you will need to sign an embryo discard form. We encourage you to consider donation to research to help us in our quest to learn more about these embryos and about IVF in general so we can continue to advance the field and help other patients, now and in the future. Again, there is no wrong decision, it is just important to make an informed decision.
The third option: POSTPONE, is to leave the embryo in storage and not to use it as a back up if your normal embryo or embryos do not survive the thaw (that would be the first option, Transfer). The advantage of this is that as we learn more about mosaic embryos, you may want to consider using your mosaic embryo in the future. The disadvantage of this is that you will need to pay embryo storage fees each year. If you have other normal embryos in storage this will not cost additional money, but if you do not, this will be an additional expense that may factor into your decision. Again, there are no wrong answers..
Genetic analysis of embryos is advancing at a rapid pace. We don’t have all the answers, but hope this article will help clarify the decisions that you will need to make if you have a mosaic embryo. Please stay tuned as this area of reproductive medicine is advancing rapidly and recommendations and options may change in the near future.