Most low-risk pregnancies include one to two routine ultrasounds. The American College of Obstetricians and Gynecologists recommends at least one standard ultrasound, typically performed between 18 and 22 weeks. Many providers also order an earlier scan in the first trimester, bringing the total to two for an uncomplicated pregnancy. If complications arise or risk factors are present, that number can climb significantly.
The Two Standard Scans
The first routine ultrasound is a dating scan, usually done between 8 and 14 weeks (most often before 12 weeks). The sonographer measures your baby from head to bottom, a measurement called crown-rump length, to estimate gestational age and narrow down your due date. This scan also confirms how many babies you’re carrying and checks for a heartbeat. Early in pregnancy, the baby is still too small for the sensor on your belly to pick up clearly, so this scan is often done with a transvaginal probe. After about 6 weeks, both approaches can work, but transvaginal imaging tends to give clearer pictures at this stage.
The second routine scan is the anatomy scan, done between 18 and 22 weeks. This one is more thorough and typically takes about 30 minutes. The sonographer examines your baby’s bones, heart, brain, spinal cord, face, kidneys, and abdomen. They also check the placenta’s position and blood flow in your uterus. This is the scan where many parents learn the baby’s sex, though its real purpose is screening for structural abnormalities.
When You Might Need More
Two scans is the baseline for a healthy, uncomplicated pregnancy, but several situations call for additional imaging. A third-trimester growth scan is indicated when there’s a mismatch between your belly measurement and how far along you are, which can signal that the baby is growing too quickly or too slowly. Conditions like gestational diabetes, high blood pressure, carrying multiples, or a history of pregnancy complications often mean your provider will schedule scans every few weeks in the third trimester to monitor growth and fluid levels.
Some women end up with five, six, or more ultrasounds over the course of their pregnancy. This isn’t unusual and doesn’t mean something is wrong. It simply reflects that your provider wants closer monitoring. If your placenta is positioned low at the anatomy scan, for example, you’ll likely get a follow-up scan later to see if it has moved. Bleeding in early pregnancy, uncertain dates, or a previous cesarean delivery can all trigger additional imaging.
What to Expect During the Scan
For transabdominal ultrasounds (the kind done on your belly), you may be asked to drink two to three glasses of water about an hour before your appointment and avoid using the bathroom beforehand. A full bladder pushes the uterus into a better position for imaging and creates a clearer picture, especially earlier in pregnancy. Later in the third trimester, your baby is large enough that a full bladder is less necessary.
The scan itself is painless. A sonographer applies gel to your abdomen and moves a handheld sensor across your skin. They may be quiet for stretches while concentrating on specific structures, which can feel nerve-wracking but is completely normal. If they can’t get a good view of a particular area because of the baby’s position, they may ask you to walk around or come back another day.
Are Ultrasounds Safe?
Diagnostic ultrasound has no confirmed harmful biological effects at the energy levels used in standard prenatal scans. Unlike X-rays, ultrasound doesn’t use radiation. It works by bouncing sound waves off tissues to create an image. That said, ultrasound does transmit a small amount of energy in the form of heat, which is why medical guidelines follow a principle called ALARA: as low as reasonably achievable. Sonographers keep the machine’s power settings and scan duration to the minimum needed for a clear image.
Professional guidelines from the American Institute of Ultrasound in Medicine specify that all pregnancy scans should start at low output settings and that higher output should only be used when necessary to get adequate images. Protocols that keep output within standard ranges reflect minimal risk. The key takeaway: ultrasounds ordered by your provider for a medical reason are considered safe.
Why Keepsake Scans Are Different
Commercial 3D and 4D ultrasound businesses offer “keepsake” photos and videos of your baby, but the major medical organizations advise against them. The person operating the machine at a commercial studio is focused on getting a photogenic image, not assessing your baby’s health. They may not have the same training as a certified sonographer, and if they notice something concerning, they’re unlikely to be equipped to counsel you or arrange follow-up. This can lead to unnecessary anxiety or, worse, false reassurance.
There’s also a practical safety concern. Getting a good 3D photo often takes longer than a diagnostic scan, and you may need multiple sessions. Each one increases the total energy exposure to your baby. While a single extra scan is unlikely to cause harm, the cumulative effect of repeated, prolonged sessions without medical oversight runs counter to the ALARA principle that governs clinical ultrasound use.