We found out about ours at the 20 week ultrasound. Huge surprise. I didn't feel much movement b/c my placenta was anterior. I did remember being slightly more nauseated at the beginning, but I thought that maybe this was a boy since I had only had girls....haha, was I ever wrong.
My brother's gf told me the day before my u/s that she thought maybe there were 2 in there as I was bigger than she remembered when I had my 3rd. I told her no, it was probably b/c this was my 4th baby and my muscles were pretty much nonexistant. Wrong again!! LOL!
I remember the doctor being able to palpate 2 babies and once they reached a certain week of pregnancy, they were pretty much stuck in the same positions. I knew who was who and could tell when my dd had hiccups as hers were different from my ds' whose hiccups were stronger.