I received an email today and I hope that the sender wont mind if I answer it here, as it's a common question and it would be good to get some comments
I read your post about teratomas and what happens when you absorb your twin into your body, but can you absorb your twin without getting a teratoma? What exactly happens if the twin isn't miscarried? I've done multiple searches on this subject, and I can't find much of anything that answers my question.
If this is your question, dear reader, then I suggest you research a little further using Google scholar to make sure you get good quality information. The key words are:
If your twin was not identical, then if there was not a miscarriage there may have been some bleeding, and if not any bleeding then perhaps your twin died before being properly implanted.
If you have a very strong feeling that your twin is insoe you and that you are two very different people, you may be a chimera and have two sets of DNA. That may give you eyes of a different colour or a patch of a different colour in one eye:
There is plenty more about all this in Womb Twin Survivors, with lots of references to scientific papers.
If stem cells from your twin somehow were taken up inside your body ( this has to happen at a very very early stage!) and didn't develop into a dermoid cyst or teratome but in fact grew into a kind of recognisable tissue, such as skin cells or ovaries, that make you a mosaic. People with vitiligo are mosaics and have skin in different coloured patches. To help you to imagine this, here is an illustration from A Healing Path;