I never heard of this until someone mentioned it in the 12 week u/s gender post. After looking it up, apparently it's based on the side of the uterus the placenta is implanted. Left side = girl and right side = boy. I also read that the transvaginal u/s would be the one to read and it would not need to be flipped, it would be left is left, right is right.
Anyone heard of this before or had it be right with their LO? I find it so interesting. It might be fun to keep track of it on here and see what the rate of correct outcomes is.