Repeating genetic testing in mosaic embryos is an effective way to achieve a more accurate diagnosis
Mosaic embryos are considered to have reproductive potential when they possess two different cell lines: one with a normal number of chromosomes ("euploid") and another with some kind of chromosomal alteration. Although normal births have been reported after the transfer of mosaic embryos, only limited information is available on the clinical implications of such transfers. The decision to transfer mosaic embryos in assisted reproduction treatments thus remains controversial, and in any case, appropriate genetic testing must subsequently be conducted to assess the type of chromosomal abnormality detected and chromosomes involved.
A study conducted by Lluc Coll, biologist at the Reproductive Medicine Service at Dexeus Women's Health attempted to determine whether performing a second biopsy in mosaic embryos can provide additional information allowing a more comprehensive assessment of their use in assisted reproduction.
Between January 2015 and April 2017, patients with mosaic embryos were given the option to have their embryos biopsied for a second time in order to obtain additional information on their genetic make-up. Nineteen patients agreed to a second biopsy on a total of 23 vitrified mosaic embryos. Blastocysts which survived and developed properly after thawing were biopsied and re-frozen pending the results of genetic tests.
All blastocysts (23/23) survived thawing; of those, 87% developed favourably, thus allowing a second biopsy to be performed (20/23).
Diagnosis was possible in all 20 retested blastocysts. Of the 11 who had shown whole chromosome mosaicism, 27.3% had a second euploid biopsy. On the other hand, the second biopsy found 77.8% of the blastocysts initially diagnosed with segmental mosaicism to be euploid.
The authors of the study concluded that repeat biopsy in mosaic embryos is an effective approach to achieve a more accurate diagnosis and give patients better genetic counselling. Also, if considering the transfer of mosaic embryos, those with segmental mosaicism should be prioritised. However, regardless of the results obtained in the second diagnosis, the embryos should still be considered as mosaic embryos.
Scientific poster: Mosaic embryons: is it worth re-biopsying them?
Coll L1, Parriego M1, Boada M1, Vidal F2, Tresanchez M1, Coroleu B1, Veiga A13
1 Reproductive Medicine Service. Department of Obstetrics, Gynaecology and Reproductive Medicine. Dexeus University Hospital
2 Cell Biology Unit. Autonomous University of Barcelona, Bellaterra
3 Stem Cell Bank. Barcelona Centre for Regenerative Medicine
See scientific poster (PDF)