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Mosaic Embryos and Ivf

October 24, 2018
Katie Visco

Ivf testing has come along way since the first birth of a baby via Ivf. The advancements in Ivf procedures have helped millions in conceiving for infertility, but debates have been stirring over “mosaic” embryos, embryos with both normal and abnormal cells. Mosaic embryos can heighten the chances of miscarrying or other serious developmental defects.

The mosaic of IVF

daughter and close up of pregnant mom

Typically the preimplantation genetic screening, or P.G.S., and implantation of embryos are reserved for only the best, healthiest embryos. When embryos are collected, they are tested for quality and any abnormalities. One of these abnormalities is mosaic embryos. Mosaic embryos are embryos with both normal and abnormal which we could tell from the precision of P.G.S. from a few years ago. Now with the next-gen sequencing of P.G.S., we have a much sharper image of the mosaic embryos and we can now see these mosaic embryos during the active IVF cycle. This technology has found that 20% of embryos are these mosaic embryos. The percentage of these mosaics embryos only increase with age.  This can be troubling as these mosaics can increase your chances of miscarriage and other serious developmental defects.

Research and Conceiving

pregnant woman

Embryos with the correct number of chromosomes, called euploids, have a higher chance of successful pregnancy when compared to aneuploids, the ones with incorrect numbers of chromosomes. Research is still ongoing and it is difficult to say exactly what these mosaics will do to your pregnancy. The Preimplantation Genetic Diagnosis International Society or PGDIS recommends the prioritization of mosaic embryos for transfer by their levels of mosaicism and what chromosomes are present in the embryo. The mosaic embryos that are the top priority have the chromosomes: 1, 3, 10, 12, and 19. These have the lowest risk of the frightening outcomes we’ve talked about. The next possible group of chromosomes: 4, 5, and 17, xyy. These chromosomes are slightly more dangerous as they increase the likelihood of a miscarriage slightly. Chromosomes 2, 7, 11, 17, and 22 contribute to a higher risk of miscarriages or a low risk of UDP which is affected by chromosomes 7 and 11. Chromosomes 6, 9, and 15 are the 4th tier and second to last chromosomes that are prioritized during the IVF process. Chromosomes 8, 20, 47, xxx, and 47, xxy should only be considered after a long discussion with the parents about the possible clinical issues. These chromosomes carry a higher risk of fetal involvement and a slightly increased risk of miscarriage and viable aneuploidy. The chromosomes to avoid are 13, 14, 16, 18, 21, and 45, X. These chromosomes have a very high risk of all of the previously mentioned outcomes possible from transferring these embryos for fertilization.

You and Mosaics

The idea of mosaic embryos could be scary but it’s important to know what you’re up against. Pregnancy isn’t ever an easy thing for anyone. Mosaics are another huddle of conceiving. Luckily with advanced technology, we can now pinpoint what embryos are abnormal and are able to make smarter decisions with the transferring of embryos.


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