An abdominal scan is usually painless except for the mild discomfort of the transducer pressing on your tummy if you have a very full bladder. If you are in pain, tell the sonographer. She may ask you to half empty your bladder, which will make the scan more comfortable.
You shouldn't be asked to fill your bladder for scans in the third trimester. At this stage, your baby is much bigger and the amniotic fluid around him will help conduct the echoes to create the image on the screen.
Some women prefer a vaginal scan, as it's best done with an empty bladder. There's no need to feel embarrassed as the sonographer does these scans every day. She’ll cover you with a sheet, and if you relax your muscles to allow the transducer to slide in easily, it shouldn't be uncomfortable.

Do I have to have an ultrasound?
Most women in the UK have at least one scan during pregnancy, but you don't have to have one. Scans give useful information about your pregnancy, and most women find them reassuring.
If your midwife recommends a scan and you'd rather not have one, ask her to explain her reasons. The final decision will always rest with you.

liver ultrasound machine