Low Risk of Fetal Chromosome Abnormality After Mosaic-Embryo Transfer

NEW YORK (Reuters Health) – Embryos classified as mosaic are capable of producing healthy babies and should be considered for transfer when a euploid embryo is not available, say fertility specialists.

Mosaic-embryo transfer (MET) following preimplantation genetic testing for aneuploidy (PGT-A) – the process of screening in vitro fertilization (IVF) embryos for chromosome abnormalities prior to transfer – has become more common based on mounting evidence that these embryos have reproductive potential.

Often cited risks associated with MET include the possibility of an ongoing pregnancy with chromosomal syndrome, despite a lack of documented cases in which this has occurred.

Dr. James Grifo and colleagues at NYU Langone Fertility Center in New York City reviewed all MET cases occurring at their center since September 2015 in which an ongoing pregnancy was documented.

Of the 35 patients who had mosaic embryos transferred, none of those fetuses had chromosomal abnormalities, suggesting that the risk for chromosomal syndromes associated with MET is “likely overestimated,” the team reports in an abstract presented at the American Society for Reproductive Medicine (ASRM) annual meeting.

“All of the babies that we’ve had from mosaic embryos have been born healthy and they’re growing fine. Some of them are over 6 years old so we’re now much more comfortable transferring these mosaic embryos,” Dr. Grifo told Reuters Health by phone.

Mosaic embryos have been “making babies from the beginning of time. No one even knew they were mosaic because we didn’t have the sensitive tests that we have now,” he noted.

“Our data and our collaborators data show that this finding of mosaicism is really not as scary as we thought originally,” Dr. Grifo said. “Only about 8% to 10% of embryos come back as mosaic but for some patients it’s their only chance.”

Dr Grifo said genetic counseling about MET is essential and should address benefits, limitations and risks of prenatal diagnosis, including the potential of an unrelated variant of uncertain significance (VUS) and procedure-related risk of spontaneous abortion.

Currently it remains unclear whether specific types of prenatal diagnostic tests outweigh the risks. One spontaneous abortion occurred due to amniocentesis-related complications.

At the NYU Langone Fertility Center, “every single patient participates in genetic counseling. We are very open and honest with our patients about what we know and what we don’t know. They hear the options and they make really good choices and then we help them through making sure they have a good outcome,” Dr. Grifo told Reuters Health.

They NYU team says further study is needed to determine whether specific types of mosaic results are associated with different risks, as well as the psychological impact of prenatal diagnosis after MET on patients.

SOURCE: https://asrmcongress.org/ American Society for Reproductive Medicine (ASRM) annual meeting, held October 17-20, 2021.

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