Oh, mosaics are a hot topic of debate. I’ve got one 50% segmental mosaic with a chromosome 17 microdeletion and don’t really know what to do with it. Had a consultation with a genetic councillor, which made my understanding clearer but didn’t give me full confidence. According to the councillor:
* the industry have moved from not transferring / or transferring mosaics only in some cases (eg. low level mosaics) to transferring them regardless if this is the only option
* recent research shows that the outcome of transferring mosaics is the same/very similar to transferring euploid embryos regardless of the level of mosaicism with an exception of high level full chromosome mosaics (i.e. not segmental) where only a small difference was observed
* there is no evidence that transferring mosaics results in higher occurrence of abnormalities in children compared to euploids. At the same time, there is not enough research on it
* there is also everyone’s favourite “embryo can correct itself”. This is not true for aneuploids, but could potentially be true for mosaics. This are a couple of theories at the moment with not enough evidence to support the case but nonetheless. Mosaic self-correction theories are:
- abnormal cells stop dividing leaving just normal ones
- abnormal cells are “pushed” to placenta. I guess this may be based on the fact that there exists such thing as confined placental mosaicism (CPM) where placenta is mosaic but the baby is full euploid.
Finally and most importantly, for mosaic transfers genetics councillors recommend to do amniocentesis during pregnancy instead of other tests for abnormalities as for mosaics these tests (eg. NIPT) can show false positive results especially if mosaicism affects chromosomes 13, 18, 21 (Down, Edward, Patau). I believe amniocentesis is also the only test that can identify CMP. The trouble with amniocentesis though is it comes with a certain risk of miscarriage, small but not completely negligible.
Thank you so much for you comment! So informative!
We had a chat with our genetic councillor today who strongly encouraged us to transfer ours. She said it had a maximum of 30% mosaicism where as full euploid have up to 20% so she said it’s basically a euploid.
She mentioned about the cells being “pushed” to the placenta and gave us some really positive stats re: transfers. She also encouraged amniocentesis if the pregnancy progressed due to my age (40) and our history.
Thank you so much I hope you come to a decision re: your embryo xx Good luck
I’m so pleased you had a good discussion with them today. On reading your post I was about to comment that you can find out the % and it may be not far off a euploid! Good luck 🙏🩷
my 10 month old was a low level mosaic embryo. It was chromosome 12. Nowadays there is so much evidence to show there is no risk (other than miscarriage) in transferring a low level mosaic embryo. It doesn’t matter what chromosomes are affected anymore as it would be so rare to have a mosaic embryo born with a chromosomal issue. And there is much lower risk than in an untested embryo.
We didn’t do an amniocentesis, nor did we do an NIPT. An amniocentesis has a 1 in 200 chance of causing miscarriage and the chance of our mosaic having an issue was far lower (like 1 in 4000) so we didn’t want to risk it. If my 12 week scan and nuchal test had showed a higher risk then we would have considered it but it was saying 1 in 4000). Though they have to ‘suggest it’ and we wouldn’t have been suggested it if our embryo was untested and yet there would be a far higher chance of issue. Make it make sense 🙈
Anyway I’m a huge supporter of mosaic embryos. We had two euploid embryos fail and then our mosaic finally worked, we have 4 other embryos frozen and they are all ‘mosaic’, so we will definitely be trying them for a sibling.
happy to help in any way, I did a ridiculous amount of research when we were going through this so I feel very knowledgeable in this area!
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