Gender at growth scan?

I know the point of all ultrasounds, especially one with growth in the name is to see how the baby is doing, and to check to make sure everything is okay. That said, would it be rude if I asked them if they could determine the gender? Not have them go out of their way to look or anything, but if they happen to be taking measurements and see something? Baby's legs were crossed at our 20 week scan and I just want to know without inconveniencing the ultrasound tech.