It takes approximately one hour to fill your bladder after drinking 36 ounces of fluid, according to Union Hospital in Maryland. Pelvic and fetal ultrasounds require a full bladder for the procedures, and you can empty your bladder after ultrasound images are obtained.
Empty the bladder two hours before an ultrasound, and then start drinking 32 to 36 ounces of liquid up until one hour before the ultrasound appointment. Viable liquids include water, juice and decaffeinated coffee or tea, notes Union Hospital. Do not drink soda, caffeinated beverages or milk. Finish the liquid one hour before the appointment so the bladder has 60 minutes to fill completely before the appointment. Drink 20 to 24 ounces of liquid if you are in your third trimester of pregnancy.
Do not use the bathroom until after the ultrasound technician obtains necessary images of the pelvis or fetus. Ultrasound examinations only take about five to 10 minutes, and then you can relieve your bladder in the bathroom, according to Union Hospital.
If you are not sure how long your bladder takes to fill, experiment at home. Drink some water and time how long it takes before your bladder feels full, explains 101 Diagnostics. For abdominal ultrasounds, patients should cease eating about four hours before the appointment to obtain accurate readings.