I was told 1 L of clear fluid 1 hour before the scan.When I did this with DS, the tech burst out laughing when she saw the baby.I believe that around 11 or 12 weeks your uterus pops up above your pelvic bone, which is why you really don't need a full bladder by that point to help "push" it up and out so the tech can get a good look like you have to early on.
It's to make the ovaries and other non-baby measurements easier to do.So, if you get that taken care of earlier (at another ultrasound), it makes sense that they wouldn't need you to do that at a 20-wk u/s.If the point is just to fill up the bladder so that the uterus pops out of the pelvis more then I'm guessing the total 32 ounces probably isn't necessary for me (it seems to be popping out enough already) but if I can drink it without feeling really uncomfortable I will just to make the ultrasound technician's job as easy as possible for her.I just had mine at 18w, and the tech actually asked if I had to use the restroom before she did any of the ultrasound--an empty bladder was no problem for her. They sent me to pee to the count of 40 not once or twice but three times!!
Then I could see the difference, he was stretching out and bouncing all over the place. The tech told me that if you normally drink a lot of fluids and stay well hydrated, you don't need to have nearly as much before the scan.I drank about a quarter to a half a liter in the car on the way there and the doctor who did the ultrasound didn't comment about the fullness (lack of fullness) of my bladder at all.I can't imagine what would be "comfortably full" though halfway through a second (or more) pregnancy...I just drank my usual amount of liquid, and they were able to see everything perfectly fine.As a matter of fact, the u/s tech at the 12 week asked me to empty my bladder a bit because she said it was a bit too full.I have my 20 week scan today and I guess I'll aim for an amount in between my two previous experiences.