What you need to do before an ultrasound depends entirely on which body part is being scanned. Some ultrasounds require fasting, others require a full bladder, and some need no preparation at all. Your imaging center should give you specific instructions when you schedule, but here’s what to expect for the most common types.
Abdominal Ultrasound Prep
If your ultrasound is focused on your abdomen, you’ll typically need to fast for 8 to 12 hours before the exam. That means no food and, in most cases, limited drinks. The reason is straightforward: eating triggers your digestive organs to contract and move, which can distort the images. An empty stomach gives the technician a much clearer view of your liver, pancreas, spleen, and surrounding structures.
During your fast, you can usually drink clear liquids like water, black coffee, or plain tea. Avoid anything with fat or sugar in it, as these can still trigger digestive activity. If you take daily medications, ask your provider whether it’s okay to swallow them with a small sip of water. Most practices allow this, but the answer can vary depending on what’s being examined.
Gallbladder Ultrasound Prep
Gallbladder scans have stricter rules than a general abdominal ultrasound. You need to fast for at least 6 hours beforehand, because eating causes the gallbladder to contract and release bile to help digest food. If you’ve eaten within that window, your gallbladder may appear shrunken or abnormal on the images, potentially leading to an inaccurate reading or a repeat exam. Clear liquids without fat or sugar are still fine during the fasting period.
Pelvic and Obstetric Ultrasound Prep
Pelvic ultrasounds flip the script: instead of fasting, you need to show up with a full bladder. A filled bladder pushes your intestines out of the way and creates a better window for the sound waves to reach your uterus, ovaries, or bladder. The standard instruction is to drink at least 24 ounces of clear fluid (about three cups) at least one hour before your appointment, and then hold it until the exam is finished.
This can be genuinely uncomfortable, especially if your appointment runs late. A helpful strategy is to start drinking right at the one-hour mark rather than earlier, so you’re not in agony by the time you’re called back. Stick to water or another clear fluid rather than juice or soda.
Transvaginal Scans Are Different
If you’re having a transvaginal ultrasound (where the probe is inserted internally rather than pressed against your abdomen), the bladder instructions may be reversed. Some providers want your bladder full, others want it empty, because the fullness of your bladder changes how your organs appear on the screen. Follow your provider’s specific instructions for this one, as there’s no universal standard.
Kidney and Bladder Ultrasound Prep
Kidney scans also require a full bladder. The instructions are similar to a pelvic ultrasound: drink 24 ounces of water one hour before your appointment and don’t use the bathroom until the test is done. A full bladder helps the technician see the kidneys, ureters, and bladder wall more clearly. If you’re having both a kidney and abdominal scan in the same visit, ask which set of instructions takes priority, since one requires fasting and the other requires drinking.
Vascular and Heart Ultrasound Prep
Vascular ultrasounds, including carotid scans (which check the arteries in your neck) and echocardiograms (heart ultrasounds), generally require no preparation at all. You don’t need to fast or drink extra water. The main consideration is what you wear. For a carotid ultrasound, choose a shirt with a low neckline so the technician can easily access your neck. A turtleneck or high collar means you’ll likely need to change into a hospital gown. Skip necklaces and dangling earrings that could get in the way of the probe.
What to Wear
For any type of ultrasound, wear loose, comfortable clothing. Depending on the area being scanned, you may need to lift your shirt, lower your waistband, or change into a gown. Two-piece outfits are easier to work with than dresses or jumpsuits. Leave jewelry and valuables at home, especially anything near the scan area. Jewelry doesn’t interfere with the ultrasound waves the way it does with an MRI, but it can physically block the probe or need to be removed and stored during the exam.
Prep for Children’s Ultrasounds
Preparation for kids depends on the type of exam, just as it does for adults. When you schedule a pediatric ultrasound, ask specifically about eating and drinking instructions, since fasting requirements may be shorter for younger children. Dress your child in loose, comfortable clothing they won’t mind pulling up or adjusting. For younger kids, bringing a favorite toy or comfort item can make the process smoother. Ultrasound is painless and doesn’t involve radiation, so the main challenge with children is keeping them still long enough for clear images.
Day-of Logistics
Most ultrasound appointments don’t require you to bring anything special. You won’t need to arrange a ride home afterward since there’s no sedation involved, and the exam itself typically takes 20 to 45 minutes. Arrive a few minutes early to handle any paperwork, but there’s no need to budget the kind of extended check-in time you’d plan for a hospital procedure.
If you accidentally ate before a fasting ultrasound or forgot to drink water before a pelvic scan, call the office before heading in. They may be able to push your appointment back or give you time to drink water on-site. It’s better to reschedule than to go through an exam that produces unusable images.