Babies with trisomies don't tend to live very long after birth and have an extremely low quality of life.
Your sister should start receiving counseling right now. She will soon be experiencing a lot of heartache and depression once the baby is born.
Hey, I'm currently pregnant with a baby that has Trisomy 14 Mosaicism.
The pp is right in that full blown Trisomies most don't survive. However, mosaicism could be anything from barely noticeable depending on what's affected in the body to a death sentence as well.
We decided not terminate, and I'll be honest, it's hard. But I've also made it farther than any doctor ever said we would. I have one doctor telling me things are relatively fine and another telling me baby is going to die. Not knowing is hard either way.
You can check out my blog for further information and maybe it will help you understand what she's going through.
If you want to talk or want an email address send me a private message and I'll be glad to respond.
I also wanted to add make sure your sister does lots of research and asks lots of questions.
Our genetic counselor told us baby was going to die and it was so crazy rare that we should terminate. She also said amnios were 99% accurate.
We found a well researched doctor that gave us a better prognosis and explained that while amnios are 99% accurate in most cases, it doesn't apply to mosaicism. In fact a lot of times mosaicism can be detected in amniotic fluid but not in baby at all. That and the concentration of mosaic cells is often higher in the amnio fluid than the actual baby.
So make sure she asks around and does her research.