Glucose test?

Jenna • 20, single, FTM. Baby boy due 10/24💙
Might be a silly question. 
When do you typically go in for the glucose testing? Where they give you a sugary drink and do blood work an hour later? It was mentioned at my last appt I would do it at my anatomy scan (tomorrow) & I'll be 20 weeks 5 days. Just seems too soon for some reason! I may have misunderstood as well. Must curious! 
20, FTM