So, I remember back in high school I read about this guy that had a twin in-utero, but that twin died early on. Typically when it happens in the 1st trimester this is called Vanishing Twin Syndrome (VTS). It's estimated that 1 in 8 pregnancies may actually have a twin, but statistically only 1 in 70 births are twin births. Basically, what happens is that the lost twin is absorbed by the mother and the surviving twin. We wouldn't know much about VTS if it weren't for early ultrasound.
Anyway, so this guy was the surviving twin. He was getting a lot of headaches and the doctors discovered a tertoma tumor on his brain. A tertoma tumor is a tumor made up of the parts of the lost twin. Pretty freaky, huh? Well, this tumor was making him do really bad things and the docs thought it was affecting his brain because of the location of it. So, they removed the tumor and the guy was able to live a pretty normal life without the headaches... for awhile anyway.
With the tumor removed this "vanished" twin was able to come to life and somehow came back as a full grown man looking just like the surviving twin. He was really bitter about losing his life up to this point and decided to take over the life of the surviving twin, but that meant killing the survivor. Not only was he trying to kill his surviving twin, he also brutally murdered other people in the surviving twin's life. This tumor definitely turned into the infamous "evil twin." Anyway, in the end, good twin killed bad twin and while it was a horrific experience, he was able to move on with his life. It was really difficult, however, to explain the murders of those around him, since his evil twin left behind fingerprints, dna, and other evidence that pointed to him. Still, everything was resolved. No, this story wasn't in a newspaper. It was "The Dark Half" by Stephen King. Still, these stories have to come from somewhere, right? ;)
Anyway, I was wondering, do you think that may happen to my twins if I lose the one? And if I (hopefully) keep both babies, would CVS or amnio be able to detect which one is the evil one?