No you can only tell by looking at the genital area. We had a very experienced sonographer doing our last scan and she couldn't tell until dd shoved against the screen. She had been turned away at the start of the scan.
We don't want to find out. We're just guessing. Dp was joking about what he saw as he didn't look. It was purely just for fun.. We have a 4d one booked but will tell them we don't want to know ( unless by then we change minds lol)