Maybe it was a paristic twin?

I had the same thing! I asked my doc at my 6 week post partum and they have no idea why. They said it's possible it was a vanishing twin, but as I had my first u/s at 5w preggo and saw only 1 they're really not certain. They say it's rare but does happen. You're actually the first other person i've heard of that it's happened to. I thought I was weird. Lol

A lady that works for the agency I work for is in her 50's. She is a .Big woman. She started having more problems moving around. She got winded more easily, and was having a lot of pain in her abdomen. She went to a couple of docs, got some various opinions on what could be causing all of the pain.
She was told she had a huge cyst on her ovary, so they scheduled surgery to get it out. When they got in there to remove it they found it had hair and what resembled teeth. She was told it was her twin that she absorbed while she was in embryo. They also used the term vanishing twin. It weighed 60 pounds!!!!!!!!!!!! I didn't see pics for myself, but she showed some of her peers. I had never heard of it.

oh yes, this is a rare event and I remember there was a tv program about it here in england a few months ago. I was fascinated and checked it on the net.
Found some details on: http://www.Pregnancy-bliss.Co.Uk
search for the medical term fetus in fetu. Fascinating indeed!

I just saw a thing on tlc tonight with the woman to have the biggest tumor ever removed it was 200lbs.. Freaky it coverd her all way around