This is starting to drive me bonkers, but reflecting upon a couple of things that the sonographer said at my 12 week scan I realise she had a pretty good idea of the sex of my baby - I was just so filled with relief that everything was ok that I didn't click that she was subtly trying to find out if I was interested in knowing the sex.
Although I would love to, I can't write a letter to her with an sae saying 'excuse me, but desperate to know sex and think you may know'.
chutnymary said that at 12 weeks it is something to do with the angle of the dangle see this page
If anyone knows a little about this...here is the scan picture