Study raises questions about popular genetic test for ‘abnormal’ embryos
But the new study also shows the limits of transferring such embryos. A large majority of the 144 embryos transferred by the group had only one or two chromosomal abnormalities, but the transfers resulted in 11 miscarriages in addition to eight live births.
“There are a lot of miscarriages in that ratio,” said Laura Hercher, director of student research in the genetic counseling program at Sarah Lawrence College.
The PGT-A test is used to screen for aneuploidy, which is when an incorrect number of chromosomes – too few or too many – are detected in sampled cells. An abnormal number of chromosomes can, in severe cases, lead to genetic disabilities, such as Down syndrome. More often than not, an incorrect number of chromosomes can lead to pregnancy failures, either by preventing the embryos from implanting or by causing miscarriages.
But the problem with PGT-A, according to the study authors, is that it provides an incomplete picture that is often interpreted as a very definitive result. The test relies on sampling a handful of cells from the outer coat of the developing embryo and testing to see if each has 23 pairs of chromosomes.
“The goal of PGT was to select embryos that would give someone a better chance of getting pregnant,” said Dr. David Barad, OB-GYN at the Center for Human Reproduction and co-author of the study. “But doing genetic testing doesn’t improve the embryos, it just gives us an idea of who they are.”
Although moving forward with the use of these abnormal embryos may carry some risk, the authors of the new study, who were all connected to the clinic performing the transfers, say that viable embryos are currently ignored, leaving many women to believe they have no other options to achieve pregnancy.
“The miscarriage rate is about what you’d expect at such an advanced age,” clinic director and study co-author Dr. Norbert Gleicher said in an email. He added: “Ask the women what they prefer. A risk of miscarriage or no chance of having a baby. The answer will be clear.