I had a scan at nearly 23 weeks and we didn't want to know the gender. The sonographer therefore said she wouldn't look and didn't scan that area - there was no way we could tell.
And when she printed scan pictures for us, she printed one of head & body, then another of legs!!!
The amount of detail you can see is amazing, so I guess if you are looking and get to see in the right place, it might be obvious....!
Good luck at the scan
LBxx