Mosaicism can occur on several levels: gene, sub-chromosome, and chromosome. Sub-chromosome refers to mosaicism of chromosome segments rather then the entire chromosome. Only the sub-chromosome and chromosome levels are considered in preimplantation genetic screening.
Clinical outcome is variable, although only a minority of mosaic embryos result in healthy pregnancies. Compared to a euploid embryo, a mosaic embryo is much more likely to result in implantation failure, miscarriage, or a newborn affected with a genetic disorder.
The impact of mosaicism in IVF is still in preliminary research stages and should be considered carefully when making a clinical decision. Genetic counseling is highly recommended when considering the transfer mosaic embryos. Studies recommend that patients undergo an additional IVF cycle to obtain a euploid embryo instead of transferring a mosaic embryo.