Hi, I have just had a little girl (3 weeks old on Thur) and she was born with an extra little bit of a thumb.. was`nt picked up on the scans, probably because it is small... about the size of the tip of her little finger... apparently it is very common and she will have it removed when she is about 6 months old. We just think she is extra special
I`m not sure what the 5th on your scan means but I wouldnt worry too much.
All the best for the rest of your pg.