I'm huge!!!
Yesterday someone asked me if I was having triplets (I have the question about twins everyday). I told the person that maybe, just maybe I would be having triplest. I've had 3 ultrasounds and they always just see one baby. Maybe it's a different baby eachtime...... I left the person very confused....
...and no, I don't think women carry twins without knowing it, if the have ultrasounds. I did here about a lady just last month who wanted a natural pregnacy and birth. She declined ultrasounds and had a homebirth with a midwife. She had twins, without knowing she was pregnant with 2 babies. I guess that was pretty common before ultrasounds.