WHOA! So apparently, this Vanishing Twin Syndrome thing is totally for real. Since they’ve started doing more ultrasound early in pregnancies, they have begun to realize that statistically, something like 1 out of every 8 (some say 6) pregnancies starts out as a twin. But only like 1 out of 70 births are actually twins. So this means that all the other ones are getting absorbed, or otherwise spontaneously aborted. That’s totally nuts! Here’s a totally gross quote under the heading: “what happens when the twin doesn’t really vanish?”

Sometimes, remnants of the inviable fetus are found in the mother, placenta or surviving twin. This is most likely to occur during the second or third trimester. Although usually the fetus will be partially resorbed and retained, the death of one twin at around 15 - 20 weeks may result in a fetus papyraceous, a tiny paper-like, flattened fetal remnant. A tertoma tumor containing bone, hair, teeth or tissue fragments is also an indication of a Vanishing Twin.

Another spot defines ‘fetus papyraceous’ as “a fetus which has died in utero, with subsequent atrophy and mummification.” Another site describes the other fetus as “parchment-like”. Is this freaking anyone else out?

Wow! And then you can also have a “holocardius“:

a separate, monozygotic twin represented by a more or less shapeless and unidentifiable mass; the vascular systems of the two fetuses are connected, and the circulation is accomplished solely by the heart of the more perfect twin.

Wow! That is truly sick! I’ve stumbled onto quite a bizarre world here with all this twin stuff.