The Grapevine

What Are Mosaic Embryos And Why Are They Dividing IVF Experts?

Mosaic embryos have been subject to much debate in the medical community. But what exactly are they and why is their use in IVF treatment considered to be a controversial one?

In vitro fertilization or IVF is a type of assisted reproductive technology used by those facing problems in conceiving due to infertility. In the procedure, the egg and sperm are manually combined in a laboratory dish to form an embryo. This embryo is then transferred into the uterus of the female patient or surrogate. 

Clinics will test the embryo and only approve it for implantation if it is found to be "normal," while the "abnormal" embryos will not be approved. But a "mosaic" embryo is one that contains both normal and abnormal cells.

Nearly 20 percent of all embryos created through IVF fall into the mosaic category, identified with the help of a test called Preimplantation Genetic Screening (PGS).

Due to the presence of abnormal cells, these embryos do carry the risk of an unsuccessful pregnancy. Nevertheless, experts note they do hold some potential to self-correct.

"Mosaic embryos are not abnormal embryos. Abnormal embryos don't make babies or pregnancies," said Dr. Jamie Grifo, director of NYU Langone Fertility Center. "Mosaic embryos have potential. They don't have the same potential as a chromosomally normal embryo. But they can make babies."

But alongside the likelihood of a perfectly healthy baby, mosaic embryos also carry a higher risk of resulting in failed implantation or miscarriage. While evidence is inadequate, further research is needed to rule out the risk of birth defects as well.

This has ignited a debate among experts on whether these embryos should be discarded or used, especially in cases when they are the last option for patients.

No doctor wants to discard a healthy embryo, but the ambiguity of mosaicism puts them in a tough spot, according to Richard Scott, founder and laboratory director at Reproductive Medicine Associates of New Jersey.

"Now we are paying attention to these mosaics, but we don’t know exactly what to do with them," he said. "A mosaic embryo does have potential for reproduction, but it could be anywhere on the spectrum from a healthy to a damaged baby, and we don’t know where."

As many as 400 fertility clinics in the United States do not even consider mosaics, opting only for normal and abnormal classifications. A survey conducted by FertilityIQ revealed 52 percent of respondents who had undergone PGS were not given any indication or informed about the potential for a mosaic embryo.

But advancements and success stories have encouraged a rising number of fertility doctors to request mosaic reporting and be open about discussing the option with patients. As more research is expected to emerge, experts hope to narrow down the exact factors that could help determine the success rate of a mosaic embryo.