finding out gender

Madison • Mama to miss Lennon Paige, born October 21, 2017
This might be a dumb question... but I'm a first time mommy and feel like I know nothing 🙈
I have an routine ultrasound booked in a month (I will be 18.5 weeks) 
And from what I have read you can find out gender this far along in pregnancy? 
So my question is:
Do I need to ask ahead of time to find out baby's gender (since this ultrasound was not specifically booked for that) or will the ask me/I can ask at that appointment? 
TIA! ❤️