Gender at 13 weeks?

I’m currently 7 weeks and went to the doctor today for bloodwork. I already have an ultrasound booked for when I’m 10 weeks (to have a set due date) then they booked me when I’m 13 weeks for another ultrasound saying they can tell me the gender of the baby..? I never heard of this, I’ve only had gender ultrasounds at 18 weeks. Anyone have it done and was it truly accurate?