Belly line

I've been told by a few friends who have children of their own that the line on your belly can sort of determine the sex of the baby? A girl I go to school with is pregnant with her 4th and it's a girl. She has 2 boys and a girl already and with both boys she had a full line and with her girls she had the line just on the lower half of her belly. My cousin is having a boy and has a full line, and another family member is pregnant with a girl and only has half. Hopefully this makes sense.