3D/4D ultrasound?

Paige

I just booked a 3D/4D ultrasound for monday!! I'm sooo excited, we didnt do this with our first & weren't going to for this pregnancy either but my dr wont give me another ultrasound and isn't positive on gender so we decided to pay out of pocket for a super cool 3D/4D!

My question is, do I go with a full bladder? Empty? How do I make sure we will get good pictures?? I will be 31 weeks pregnant