What weeks can you do the anatomy scan?

Is it just 20? Or can it be done at 19? I'm curious because my family is going away on Christmas and I want to make sure everything is good and developing correctly with my baby and of course to find out the gender haha before I go.. but I'm asking because I'm 19 weeks 2 days two days on the 23rd of December and I wanted to know is that to early? Always good morning mommies 😊