Gender reveal at KKH

Hi mummies! I'm going to do the 13 weeks scan next week (the one that tests for any chromosome defects and down syndrome etc).. I heard results will take a few weeks to be out, and will get to know the gender too. We would like to keep it a secret to do a gender reveal. Do I have to inform the doc that I'll like it to be a secret and to ask her to write the gender inside an envelope or sth?