For families undergoing in vitro fertilization, so-called “mosaic” embryos used to be unusable. Genetic testing has shown that the embryos contain both normal and abnormal cells, therefore the chance of miscarriage or serious developmental defects can be higher.
But new research and successful pregnancies are changing minds, as more doctors agree to implant the mosaic embryos, particularly when they are the last option for IVF-challenged patients. Still — they are a risk, and fertility doctors are divided on whether it’s advisable to use the embryos.
Doctors were able to see whether embryos were viable with PGS testing, which takes a biopsy of the outer layer of cells. If all of the cells are normal, the embryo is considered normal. But if there’s a mix of normal and abnormal cells, it is classified as mosaic — something that was only possible to discern in the last four years.
Through this testing, researchers discovered that around 20 percent of all embryos are mosaics, reports the New York Times, and that number increases with older mothers.
But more doctors and parents are going through with transplanting the mosaic embryos. One such family is Mary Jo and Shane Dunn, who told CBS News that a set of mosaic embryos were their last option after their only child, Luke, died of a rare cancer in 2015, when he was 17 months old.
“I just didn’t imagine continuing to live without my baby,” Mary Jo said. “It was just excruciating pain.”
They had tried IVF for two years, spending $70,000 in the process, before going forward with the mosaic embryos. Those embryos resulted in a successful pregnancy and the couple had twin girls, named Riley and Kelsey.
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While the mosaic embryos could lean abnormal and lead to miscarriage, they could also end up as a normal pregnancy. Doctors believe that the abnormal cells sometimes self-correct or get pushed out into the placenta during gestation.
“Mosaic embryos are not abnormal embryos. Abnormal embryos don’t make babies or pregnancies,” Dr. Jamie Grifo, director of NYU Langone Fertility Center, told CBS News. “Mosaic embryos have potential. They don’t have the same potential as a chromosomally normal embryo. But they can make babies.”
And the accuracy of PGS testing has also been questioned, as the biopsy comes from just a small portion of the embryo. Some doctors wonder if the biopsy, which looks at between five to ten cells, can truly represent all 200 in the embryo.
“I think the biological hypothesis that you can, from a single biopsy, determine whether an embryo is normal or chromosomally abnormal — that is flawed,” Dr. Norbert Gleicher, the director of the Center for Human Reproduction in New York, told the New York Times.
Still, other doctors are not ready to move forward with mosaic embryos because of the high risk involved, and how little research has been done on the topic.
“We really don’t know the answer to the full question of what is the probability that a mosaic embryo will result in either an affected baby or a healthy baby.” Mandy Katz-Jaffe, scientific director at the Colorado Center for Reproductive Medicine, told CBS News.