I've stupidly googled and am now really worried.
The sonographer said it looked quite substantial, and even I could see it was attached at both sides of the sac as it was pulling the sides in. It is currently at the foot end of the baby, but apparently out of reach.
She then sent me out to do my urine sample, and when I came back (with empty bladder) tried again to find it to check it had a blood supply, but couldn't find it.
So, I know they can't do anything, and I don't want to carry on googling and scaring myself, but does anyone know of any further information re risk statistics I can read? They just said they would make sure to count the number of limbs present at the 20 week scan! 