A recent study published in the journal Fertility & Sterility gives us more information about the chance of having a healthy child after transferring a mosaic embryo. The study was able to show that mosaic embryos can result in the delivery of healthy babies and the extent of mosaicism may influence this chance.
The study looked at 77 women, who had no euploid embryos available for transfer. For that reason, these women chose to transfer embryos that were considered mosaic based on preimplantation genetic screening. Mosaic means that each of those embryos were deemed to have cells with different chromosomal complements. Some of the cells had normal chromosomal arrangements, while others did not.
When compared to euploid embryos, mosaic embryos were found to have lower live birth rates, but they did still have a decent chance of resulting in a healthy baby. The live birth rate from mosaic embryos was 30.8% compared to 46.6% from euploid embryos. And, importantly, none of the babies born from the transfer of mosaic embryos were found to have evidence of mosaicism at birth.
The level of mosaicism was found to have a significant impact on the chance of having a healthy baby. Embryos with “low grade” mosaicism (at least 50% of cells were considered normal) had similar live birth rates compared to euploid embryos. The live birth from embryos with “low grade” mosaicism was 42.2%. Embryos with a high percentage of abnormal cells only had a 15.2% live birth rate.
In addition, there was not a significant difference in the miscarriage rates when comparing mosaic embryos to euploid embryos.
This study gives us important information about transferring mosaic embryos. Some of these embryos, which may have previously been deemed abnormal, have a chance of developing into healthy euploid babies. The decision about whether or not to transfer mosaic embryos should not be taken lightly though. While this study shows that euploid babies can be born from mosaic embryos, there is still no long term follow up on the health of these children.
This is a very complex issue and if you are considering transferring a mosaic embryo, you should thoroughly discuss the decision with your reproductive endocrinologist and rely on their advice to decide if your particular embryos might be suitable for transfer.