My sister has just had this problem solved at her 32 week scan!!The little bub had HER legs crossed and shoved up covering everything for both her previous scans(the 12 and 20weeks).The sonographer actually hinted at the 20 week that when their legs are kinda stuffed up into the private area then more than likely its a girl.Not sure how true it is though.But when I think about it a boy would be squeeshing all his bits!PMSL!.........sorry preggie brain thinking out loud!