The twin sister
It's a good thing the astronaut died, because if I were the twin, I would have had an abortion in order to donate part of my liver to my sister (I don't know if there's a waiting period after an abortion before you can undergo surgery)
It was clearly very early on in the pregnancy, she didn't even know yet, and she and her husband can always try again. But that's just me
I could be wrong now....but i don't think so!