Both times my wife was pregnant, I believe she had two ultrasounds per child, maybe 8 weeks apart. She was always instructed to arrive with a full bladder. I believe the extra volume helps push whatever they need to see closer to the surface so the handheld external ultrasound can visualize it better. This was always my wife's least favorite part because the technician would be putting pressure on her full bladder.
For every visit, after finishing the the external scan of her belly, the technician would tell her she could use the restroom and then, "remove her pants and panties and have a seat back on the exam table". I distinctly remember those exact words because they really turned me on to hear. For the initial external scan, she was just asked to open her pants and lower them slightly below her hips, and to raise her shirt below her breasts.
Once my wife was naked below the waist and back on the table, she was instructed to lie back with her heels in the stirrups, just like her annual exams. The tech would then insert the intravaginal wand and finish the scan.
Just after my wife's first ultrasound appointment, we were talking to a friend of hers who happened to also be pregnant with her first child, but maybe 6 months more along. She told the story of how her technician was male and that he handed her the wand, sat on the stool between her legs, and instructed her to insert the wand herself. I'm not sure if she had to insert it herself because he was male, state regulations/ law (she lived in a different state), or that's just how that technician was trained. I was so hard listening to her tell that story and visualizing it all play out.