Most healthy pregnancies include two ultrasounds: one in the first trimester (typically around 8 to 12 weeks) and a detailed anatomy scan between 18 and 22 weeks. ACOG recommends at least one standard ultrasound during pregnancy, but in practice, most providers schedule two. High-risk pregnancies can involve significantly more, sometimes every two to four weeks in the third trimester.
First Trimester: Dating and Viability
Many providers order an early ultrasound somewhere between 7 and 13 weeks. The main goal is confirming that the pregnancy is in the right location, checking for a heartbeat, and establishing an accurate due date. At this stage, the baby is measured from head to rump, and that measurement is the most precise way to date a pregnancy, accurate to within five to seven days.
Early scans are almost always done with a transvaginal probe rather than the abdominal wand you might picture. The baby is still tiny, and the transvaginal approach produces much clearer images at this stage. It’s a quick procedure, usually under 15 minutes, and most women describe it as mildly uncomfortable rather than painful.
If your provider offers screening for chromosomal conditions, you may also have a nuchal translucency scan between 11 and 13 weeks. This measures a small pocket of fluid at the back of the baby’s neck. A measurement above 3 millimeters at 12 weeks typically leads to a conversation about additional testing, though it doesn’t diagnose anything on its own.
The 20-Week Anatomy Scan
The mid-pregnancy anatomy scan, done between 18 and 22 weeks, is the most thorough ultrasound of the entire pregnancy. This is the one that takes the longest, often 30 to 45 minutes, because the sonographer is systematically checking nearly every part of the baby’s body.
The checklist includes the heart, brain, spine, kidneys, bladder, stomach, intestines, chest, and lungs. The sonographer also looks at the baby’s arms, legs, hands, fingers, feet, toes, face, lips, nose, and eyes. Beyond the baby itself, they check where the placenta is positioned, how it connects to the umbilical cord, blood flow through the cord, and the amount of amniotic fluid surrounding the baby. Your cervix, uterus, and ovaries are evaluated too.
This is also the scan where many parents learn the baby’s sex, though you can ask not to be told. If the baby isn’t cooperating (curled up, facing the wrong way), you may be asked to walk around or come back for a follow-up to get the remaining images.
Third Trimester Scans
In a straightforward, low-risk pregnancy, there’s no routine third trimester ultrasound. Your provider monitors growth through fundal height measurements (the tape measure on your belly) at each prenatal visit, and that’s often enough.
When concerns come up, like the baby measuring smaller or larger than expected, low fluid levels, or a placenta in an unusual position, your provider will add growth scans in the third trimester. These are typically shorter and more focused than the anatomy scan, zeroing in on the baby’s estimated weight and fluid levels.
If you develop complications, more intensive monitoring may start between 32 and 34 weeks. A biophysical profile, for example, uses ultrasound to evaluate five things at once: heart rate, breathing movements, body movements, muscle tone, and amniotic fluid volume. How often these tests repeat depends on the specific concern and whether results stay stable.
How High-Risk Pregnancies Change the Schedule
Certain conditions lead to a significantly busier ultrasound schedule. High blood pressure, diabetes (including gestational diabetes), obesity, thyroid disease, heart or blood disorders, and poorly controlled asthma all qualify a pregnancy as higher risk. So does a history of preeclampsia, preterm delivery, stillbirth, or a previous baby born with a genetic condition.
Problems that develop during pregnancy can also trigger more frequent scanning. Fetal growth restriction (when the baby is growing more slowly than expected), an unusually positioned placenta, or Rh sensitization all call for closer monitoring. Your provider tailors the schedule to your specific situation, but extra scans every two to four weeks in the second half of pregnancy are common.
Twin and Multiple Pregnancies
Carrying multiples means more ultrasounds, and the exact number depends on whether the babies share a placenta. Dichorionic twins (each with their own placenta, the more common type with fraternal twins) are scanned at 12 weeks, 20 weeks, and then every four weeks until delivery.
Monochorionic twins (sharing a single placenta, which happens with some identical twins) need closer surveillance because of risks related to shared blood supply. These pregnancies are scanned at 12 and 16 weeks, then every two weeks until delivery. That can mean 12 or more ultrasounds over the course of the pregnancy.
Transvaginal vs. Abdominal Ultrasounds
Most people associate pregnancy ultrasounds with the abdominal approach: gel on the belly, wand moving across the skin. That method works well from roughly 12 to 14 weeks onward, once the uterus has grown above the pelvic bone. Before that point, the transvaginal approach gives far better image quality because the probe sits closer to the uterus.
Later in pregnancy, a transvaginal scan might still be used for specific reasons, like measuring cervical length if there’s a concern about preterm labor. But the vast majority of second and third trimester scans are abdominal.
Are Extra Ultrasounds Safe?
Diagnostic ultrasound has no confirmed harmful effects at the energy levels used in medical settings. That said, ultrasound does expose the baby to energy in the form of heat, and under certain circumstances, excessive heat could theoretically cause problems. Medical facilities follow a principle called ALARA: using the lowest power settings necessary and keeping scan times as short as possible.
The concern isn’t with medically indicated scans. It’s with commercial “keepsake” 3D and 4D ultrasound studios that operate outside medical settings. The person performing those scans may not be trained to minimize energy exposure, and sessions tend to run longer because the goal is getting a good photo rather than a quick diagnostic image. The operators also aren’t trained to identify or communicate potential problems if they happen to spot something concerning. Both ACOG and the FDA advise against these non-medical scans.
If your provider orders additional ultrasounds for a medical reason, the benefit of monitoring your baby’s health far outweighs any theoretical risk from the procedure itself.