Anyone who experienced a hidden twin. Help!

Hello to those who experienced a "hidden" twin id like to know how far along you went before they "found" the twin. I was a hidden twin until my twin miscarried. And twins are on both sides of my family. I keep having dreams i have a twin hiding and am pretty big for my first pregnancy. Im 18 w +2 and haven't had a u/s since 13 w was wondering when you found your hidden twin . thanks😊