A review of published studies on Mosaic embryos states that they should not be ruled out for IVF transfers.

A new study published in “Reproductive Biomedicine Online” offers a comprehensive review on embryonic mosaicism in the field of assisted reproduction techniques. This research, led by the Genetics Interest Group of the Spanish Fertility Society (SEF in Spanish), of which Belén Lledó, Instituto Bernabeu Biotech’s scientific director, is a member, aims to summarise the current knowledge on mosaic embryos and serve as reference material for professionals in reproductive medicine.

“The main conclusion of this review of studies is that embryos with a mosaic result should not be discarded for transfer,” explains Dr Belén Lledó, “this is something very positive for patients since, by not discarding these embryos, they will have a greater number of embryos available for their IVF process and thus increase their success rates.”

Embryonic mosaicism is defined as the presence of two or more population of cells with different chromosomal endowments in an embryo, and its prevalence varies from 2% to 20%. Mosaic embryos can be classified in several ways, including the number of chromosomes affected and the percentage of affected cells. Studies indicate that mosaic embryos have lower implantation, pregnancy and clinical pregnancy rates, as well as higher miscarriage rates compared to euploid embryos (which have the correct number of chromosomes).

Some cases of persistence of mosaicism during pregnancy have been published, although more research is needed to confirm the persistence rate. “Prenatal diagnosis is highly recommended after the transfer of mosaic embryos. However, recommendations among scientific societies are contradictory regarding the methodology to be used,” says Dr Lledó.

To transfer or not to transfer: the dilemma of mosaic embryos – a narrative review

E. Muñoz, F. Bronet, B. Lledó, G. Palacios-Verdú, L. Martínez-Rocca, S- Altmäe, J. Pla