i was told the same as fionajill... the 3 lines are the vagina the labia ( from what i was told) is the middle one...

It has taken me 4 scans to get a more definate answer as to what we were having... My 18 week scan she said "if i had to guess i'd say girl"... This wasnt reassuring to me so i booked another.. The guy told me couldnt see properly...
I had another scan at 28 weeks which was told 80% chance of girl (couldnt get more then 80% as they couldnt see between the legs properly (only lines) they like to see the 3 lines and also see if there is nothing... well hanging in between....

The last one was done 32 weeks and the lady told me definatley a girl... you may have to go back for another scan later on...