Embryos that are often discarded by IVF clinics because they contain some seemingly abnormal cells are just as likely to develop into healthy babies as embryos with no chromosomal abnormalities, two new studies show.
The finding means that many people trying to conceive with IVF will have more embryos to choose from and can worry less about using slightly abnormal ones.
To select the most viable embryos for implantation, IVF clinics visually assess their shape and structure and often do genetic tests as well. This pre-implantation genetic testing is useful for identifying embryos with major chromosomal abnormalities that are unlikely to survive, but there is controversy over what to do with those that only contain a small portion of cells with chromosomal abnormalities – known as mosaic embryos.
Advertisement
About made via IVF are found to be mosaic. These embryos are often discarded or used as last-ditch options because of the perceived risks that they will miscarry or develop into babies with chromosomal conditions.
However, two studies that will be presented at the annual meeting of the American Society for Reproductive Medicine on 20 October in Baltimore, Maryland, suggest these concerns are unfounded.
In the first study, at New York University Langone Fertility Center and her colleagues monitored the pregnancies of 35 people who had been implanted with mosaic embryos. Testing at the end of the first trimester showed that .
In the second study, at Igenomix, a global reproductive genetic testing company, compared pregnancy outcomes for 484 chromosomally normal embryos, 282 low-level mosaic embryos and 131 moderate-level mosaic embryos made via IVF. Mosaicism was classified as low level if 20 to 30 per cent of cells in the embryo had abnormal numbers of chromosomes and moderate if this figure was 30 to 50 per cent.
Both types of mosaic embryos had the same chance of implanting as chromosomally normal embryos and had the same chance – about 42 per cent – of leading to the successful births of babies. Genetic testing of the newborns found , regardless of what kind of embryo they came from.
There could be two reasons for these findings. One is that mosaic embryos may have ways of removing abnormal cells as they develop. The other, which both Besser and Capalbo believe is more likely, is that testing difficulties lead to many embryos being identified as mosaic when they aren’t. Embryo testing is tricky because it involves sampling tiny amounts of DNA from the layer of cells surrounding the embryo, which are hard to analyse and may not reflect the chromosomal status of the embryo itself.
“But in any case, there doesn’t seem to be any negative outcomes associated with the transfer of these embryos,” says Capalbo.
The findings are consistent with recent work by and at US reproductive testing company Genomic Prediction, who and found that only one resulted in a child with mosaicism. This mosaicism was mild and didn’t affect the child’s health.
Our new understanding of mosaic embryo outcomes could spare IVF clients a lot of unnecessary heartache and worry, says Capalbo. Surveys have found that two-thirds of IVF clients who only have mosaic embryos , probably because of the perceived risks, and more than a third of IVF clinics in the US .
“We’re definitely seeing a shift now in thinking about mosaic embryos,” says Besser. “Everyone used to be really nervous about transferring them because we just didn’t know the risks, but now we have this data to back us up, we can provide much more reassurance to people.”
Sign up to our free Health Check newsletter for a round-up of all the health and fitness news you need to know, every Saturday
