Most pregnant women get two standard ultrasounds: one in the first trimester and one between 18 and 22 weeks. Technically, only the mid-pregnancy scan is universally recommended, but in practice, the majority of prenatal care providers also order an early scan to confirm the due date and check that the pregnancy is progressing normally. If your pregnancy is considered high-risk, you may have significantly more.
First Trimester: The Dating Scan
A first trimester ultrasound is typically done sometime between 6 and 13 weeks. Its main job is to confirm your due date, check for a heartbeat, determine how many embryos are present, and rule out an ectopic pregnancy. This scan isn’t technically required for every pregnancy, but most providers order one because ultrasound measurement in the first trimester is the most accurate method to establish gestational age, with a margin of error of only 5 to 7 days.
At this stage, the embryo is measured from the top of the head to the bottom of the spine (called the crown-rump length). Once the embryo grows beyond about 84 millimeters, around 14 weeks, this measurement becomes less reliable for dating, which is why getting the scan before that point matters.
Early first trimester scans, particularly those before 10 weeks, are often done transvaginally rather than on your abdomen. The transvaginal approach gives a much clearer image when the embryo is tiny, especially if you carry extra weight or have a tilted uterus. It’s not painful, though it can feel awkward. By around 11 or 12 weeks, most providers switch to the standard abdominal approach.
The Nuchal Translucency Screen
If you opt for first trimester genetic screening, you’ll have an additional ultrasound between 11 weeks and 13 weeks 6 days. This scan measures a small pocket of fluid at the back of the baby’s neck. A thicker-than-expected measurement can indicate a higher chance of chromosomal conditions like Down syndrome, though it’s a screening tool, not a diagnosis. This scan is often combined with a blood test to give a more complete risk estimate. Not everyone chooses this screening, so it’s not automatic.
Mid-Pregnancy: The Anatomy Scan
The anatomy scan, done between 18 and 22 weeks, is the most detailed ultrasound of your pregnancy and the one visit that’s recommended for everyone. This is the appointment people often associate with finding out the baby’s sex, but the real purpose is a head-to-toe structural survey. The sonographer works through a long checklist.
In the baby’s head, they’re looking at brain structures, skull shape, and face features including the eyes, nose, lips, and jaw. They check the heart from multiple angles to confirm it has four chambers and that blood is flowing through the right vessels. The lungs, diaphragm, stomach, kidneys, bladder, and the spot where the umbilical cord attaches are all examined. The spine is checked section by section for proper formation. All four limbs are measured, and the sonographer counts fingers and toes.
The scan also evaluates your body. The placenta’s position is noted, because a low-lying placenta can affect delivery planning. Your cervical length is measured to screen for preterm labor risk. The uterus is checked for fibroids or structural variations. A normal fetal heart rate at this stage falls between 120 and 160 beats per minute.
This scan usually takes 30 to 45 minutes. If the baby is positioned in a way that hides certain structures, you may be asked to walk around, drink water, or come back for a follow-up to complete the checklist.
Third Trimester Scans
In a straightforward, low-risk pregnancy, there’s no routine ultrasound scheduled in the third trimester. Your provider monitors growth through fundal height measurements (the tape measure across your belly) and tracks the baby’s position by feel. Many women are surprised by this, expecting a late scan to check on the baby before delivery.
A third trimester ultrasound gets ordered when something specific needs investigation: the baby seems to be measuring too large or too small, the placenta was low at the anatomy scan and needs rechecking, or the baby’s position is unclear near term. If your provider suspects reduced amniotic fluid or wants to estimate the baby’s weight before making delivery decisions, an ultrasound fills those gaps.
What Changes for High-Risk Pregnancies
If your pregnancy involves complications, the number of ultrasounds can increase dramatically. Conditions that commonly trigger more frequent monitoring include gestational diabetes, high blood pressure or preeclampsia, carrying twins or more, a history of preterm birth, kidney disease, and certain autoimmune conditions.
For high-risk patients, fetal surveillance often begins around 32 weeks and occurs at least once a week. Women with pregestational diabetes are widely monitored twice per week starting at 32 weeks. Those with moderate to severe kidney disease follow a similar schedule. These scans are often shorter than the anatomy scan, focused on specific markers like amniotic fluid levels, baby’s movements, breathing motions, and muscle tone.
When multiple risk factors overlap, the timing and frequency are adjusted based on your particular situation. Some women with complex pregnancies end up having ultrasounds at nearly every prenatal visit in the final weeks.
Are Frequent Ultrasounds Safe?
Diagnostic ultrasound has no documented adverse effects on the fetus. Unlike X-rays or CT scans, ultrasound uses sound waves rather than radiation. The FDA limits the intensity of ultrasound equipment, and sonographers follow a principle of keeping energy output as low as reasonably achievable.
That said, medical guidelines still recommend that ultrasounds be performed only when there’s a clinical reason. This isn’t because of a known danger but because the precautionary approach makes sense for any technology applied to a developing baby. Keepsake 3D or 4D ultrasounds offered at commercial studios fall outside medical guidelines for this reason. They’re not harmful based on current evidence, but they aren’t medically supervised, and the sessions sometimes last longer than a clinical scan would.
A Typical Schedule at a Glance
- 6 to 10 weeks: Dating scan to confirm due date and viability (common but not universal)
- 11 to 14 weeks: Nuchal translucency screening (optional, for genetic risk assessment)
- 18 to 22 weeks: Anatomy scan (recommended for all pregnancies)
- Third trimester: Only if clinically indicated, or weekly/twice-weekly for high-risk pregnancies starting around 32 weeks
So for a low-risk pregnancy, expect two or three ultrasounds total. For a high-risk one, the number can easily reach 10 or more by delivery. If your provider orders more scans than you expected, it usually means they want better information to keep you and your baby safe, not that something is wrong.