Most pregnant people get at least two ultrasounds: one in the first trimester and one in the second. The American College of Obstetricians and Gynecologists (ACOG) says the minimum is a single standard exam between 18 and 22 weeks, but in practice, most providers schedule two or three scans for a low-risk pregnancy and significantly more for high-risk ones.
The First Trimester Scan: 10 to 13 Weeks
Your first ultrasound typically happens between 10 and 13 weeks. The primary goals are straightforward: confirm the pregnancy is in the uterus (not ectopic), verify a heartbeat, and establish an accurate due date. A heartbeat is usually visible once the embryo reaches just 2 millimeters in size. Getting this early dating right matters because it anchors every growth measurement for the rest of pregnancy.
If you opt for first-trimester genetic screening, your provider may schedule 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 larger-than-expected measurement can signal a higher risk of chromosomal conditions like Down syndrome or certain heart defects. The scan has to happen in this narrow window because the fluid gets reabsorbed after 14 weeks.
Not every practice schedules a first-trimester ultrasound for low-risk pregnancies. Some providers skip directly to the anatomy scan if there are no concerns like irregular periods, vaginal bleeding, or a history of complications.
The Anatomy Scan: 18 to 22 Weeks
This is the big one. The mid-pregnancy anatomy scan is the most detailed ultrasound you’ll have, and it’s the one exam that virtually every pregnancy includes. The sonographer works through a systematic check of the baby’s entire body, and the appointment can take 30 to 45 minutes or longer depending on the baby’s position.
Four key growth measurements are taken: the diameter and circumference of the head, the circumference of the abdomen, and the length of the thigh bone. These establish whether the baby is growing on track for gestational age. Beyond size, the scan evaluates the brain’s internal structures, the spacing and size of the eyes, the upper lip, the four chambers of the heart and its major vessels, the lungs, the stomach, kidneys, bladder, the umbilical cord insertion point, the spine in multiple views, all twelve long bones, and both hands and feet individually. The placenta’s location is also checked to rule out conditions where it covers the cervix.
This is also the scan where you can learn the baby’s sex, if you want to know. If the sonographer can’t get a clear view of certain structures because of the baby’s position, you may be asked to come back for a follow-up.
Third Trimester Scans: Not Always Routine
A third-trimester ultrasound is not guaranteed for every pregnancy. Whether you get one depends on your provider’s practice style and whether any concerns have come up. Some providers do a quick scan around 36 weeks to confirm the baby is head-down and in position for delivery. Recent research supports 36 weeks as the best time for a third-trimester growth check, since estimated fetal weight at that point correlates more closely with actual birth weight than scans done at 30 to 33 weeks.
When a third-trimester scan is performed, it focuses on a few key areas. Fetal growth is reassessed to check whether the baby is measuring too small (below the 10th percentile) or too large (above 4,000 to 4,500 grams). The placenta’s position is re-evaluated, especially if it was low-lying at the anatomy scan. Amniotic fluid volume is measured, since too much or too little fluid can both signal problems that need closer monitoring or earlier delivery.
High-Risk Pregnancies Mean More Scans
If your pregnancy is classified as high-risk, expect noticeably more ultrasounds. The exact number varies by condition and provider, but you’ll generally have more than three. Conditions that trigger additional monitoring include gestational diabetes, preeclampsia, high blood pressure, advanced maternal age, a history of preterm birth, and growth concerns identified at earlier scans.
One specialized test used in the third trimester is the biophysical profile. It combines an ultrasound with fetal heart rate monitoring and scores five areas: heart rate, breathing movements, body movements, muscle tone, and amniotic fluid volume. Each gets 0 or 2 points for a total of 10. A score of 8 to 10 is reassuring. A score of 6 is considered uncertain and usually leads to a repeat test within 12 to 24 hours. A score of 4 or below means the baby may need to be delivered soon. Low amniotic fluid on its own, regardless of total score, triggers more frequent monitoring.
Twin Pregnancies Have Their Own Schedule
Carrying twins or multiples means a significantly busier ultrasound calendar, and the exact frequency depends on whether the babies share a placenta. Twins with separate placentas (dichorionic) are monitored with growth scans starting around 28 weeks, with visits increasing to every two weeks and then weekly as the pregnancy progresses. Twins sharing a placenta but in separate sacs (monochorionic-diamniotic) start growth monitoring earlier, around 16 weeks, because they face a higher risk of unequal blood flow between the babies.
The highest-risk category is twins sharing both a placenta and a sac (monochorionic-monoamniotic). These pregnancies require the most intensive surveillance. Monitoring starts at 16 weeks, and many providers recommend inpatient admission with daily fetal monitoring beginning somewhere between 24 and 28 weeks.
A Note on Keepsake Ultrasounds
Commercial studios offering 3D or 4D “keepsake” ultrasound videos have become popular, but both the FDA and ACOG advise against them. These sessions can last 30 to 45 minutes, far longer than a diagnostic scan, and are performed by people without medical training. Ultrasound is a form of energy that causes vibrations and a slight rise in tissue temperature. At the short exposures used in medical settings by trained professionals, this is considered safe. But extended sessions for entertainment purposes are a different situation, and the American Institute of Ultrasound in Medicine strongly discourages non-medical use.