Anatomy Scan

Mommas. I’m a first time mom and I have my anatomy scan coming up on the 31st. (I’ll be 21 weeks) Curious as to know how that appointment goes. I’m located in US and I know every doctor is different but just wanted to get a general idea. How long does it take? Do you get a 3D or 4D or just regular sonogram? I’ve heard you have to come to appointment with a full bladder? (Have not been told to do so by my OB.) Any tips? Hoping for a healthy baby girl as we miscarried our first pregnancy at 9weeks.