The anatomy scan is a detailed ultrasound performed between 18 and 22 weeks of pregnancy that checks your baby’s organs, limbs, and overall growth. It typically takes 30 to 45 minutes, and most of that time is spent with a sonographer methodically working through a long checklist of structures. Here’s what the appointment actually looks like, what they’re measuring, and what the results mean.
When It Happens and Why
Most providers schedule the anatomy scan between 18 and 22 weeks, though some guidelines extend the window to 24 weeks. This timing isn’t random. By 18 weeks, your baby’s organs are developed enough to visualize on ultrasound, but early enough that your care team can plan for any issues that come up. Scans done before 19 weeks are more likely to be incomplete simply because certain structures haven’t grown large enough to see clearly.
The scan serves as a comprehensive checkup on fetal development and also establishes a growth baseline that later ultrasounds can be compared against. Beyond the baby, the sonographer also evaluates your placenta’s position, your amniotic fluid volume, and your cervical length.
How to Prepare
Some offices ask you to drink water beforehand so your bladder is partially full, which can help with imaging in the early part of the scan. Others don’t require this at all, so check with your provider. No fasting is needed. Wear a two-piece outfit since the sonographer will need access to your lower abdomen. The appointment itself usually runs 30 to 45 minutes for the ultrasound portion, though you may wait additional time for a provider to review the images.
What the Sonographer Checks
The anatomy scan is thorough. The sonographer works through a structured list of views covering every major organ system. Here’s what they’re looking at:
- Brain: Three standard cross-sectional views of the head, checking the fluid-filled spaces (ventricles), the cerebellum at the back of the brain, and overall brain structure.
- Heart: A four-chamber view confirms that both upper and lower chambers are present, roughly equal in size, and functioning. The sonographer also checks that the major blood vessels leaving the heart are correctly positioned.
- Spine: Viewed along its full length to check for proper alignment and closure.
- Face: The lips, nose, and eye sockets are visualized, partly to screen for cleft lip.
- Abdomen: The stomach, kidneys, and bladder are all checked. The sonographer confirms that the abdominal wall is intact and the umbilical cord inserts properly.
- Limbs: Arms, legs, hands, and feet are all counted and measured.
Don’t be surprised if the sonographer spends a lot of time on the heart. It’s the most complex organ to image, and getting the right angles can require patience, especially if your baby isn’t cooperating.
Growth Measurements
During the scan, the sonographer takes four key measurements to assess whether your baby’s size matches the expected range for gestational age:
- Head circumference: The distance around the head.
- Biparietal diameter: The width of the head from side to side.
- Abdominal circumference: The distance around the belly.
- Femur length: The length of the thighbone.
Together, these give your provider an overall picture of growth. A baby measuring smaller than expected could signal growth restriction or a placental issue. A baby measuring larger might point toward gestational diabetes. One measurement slightly above or below average is rarely a concern on its own. Your provider is looking at the full pattern.
Finding Out the Sex
If you want to know your baby’s sex, the anatomy scan is highly reliable. In one study of second-trimester scans, sonographers were able to determine sex in 99.5% of cases, with 100% accuracy when a determination was made. The only case where it couldn’t be identified involved a combination of higher maternal BMI, uterine fibroids, and an unfavorable fetal position. If you don’t want to know, tell the sonographer at the start of the appointment so they can avoid revealing it.
What “Soft Markers” Mean
Sometimes the scan reveals minor findings called soft markers. These are small variations that appear in plenty of healthy babies but occur slightly more often in babies with chromosomal conditions like Down syndrome or trisomy 18. The most common ones include:
- Echogenic intracardiac focus: A bright spot on the heart, found in about 3% of fetuses. In isolation, particularly in women under 35, this is almost never associated with a chromosomal problem. One large study found that only 1 out of 626 fetuses with an isolated bright spot had Down syndrome.
- Choroid plexus cysts: Small fluid-filled spaces in the brain, seen in 1% to 2.5% of normal pregnancies. When found alone, these are typically harmless and often resolve on their own. They become more concerning only when paired with other abnormal findings.
- Thickened nuchal fold: Extra thickness at the back of the neck.
- Echogenic bowel: Bowel that appears brighter than usual on ultrasound.
- Mild kidney dilation: Slightly enlarged collecting areas in the kidneys.
- Short long bones: Limb bones measuring shorter than expected.
A single isolated soft marker in an otherwise low-risk pregnancy rarely changes your overall risk in a meaningful way. If multiple soft markers appear together, or if they’re found alongside a structural abnormality, your provider will likely recommend further testing. Hearing that something was “flagged” can feel alarming, but most isolated soft markers turn out to be nothing.
When the Scan Is Incomplete
It’s common for the sonographer to struggle with certain views. Your baby might be curled up, facing your spine, or have a hand blocking their face. Higher maternal BMI, abdominal scarring from a prior cesarean, and earlier gestational age all increase the odds of an incomplete exam. In one study, 11% of patients with a BMI over 30 and 25% of those with a BMI over 50 still had incomplete anatomy views by the time of delivery, even after multiple attempts.
If key views aren’t obtained, you’ll typically be asked to come back for a follow-up scan, usually two to four weeks later. A single repeat appointment almost always captures whatever was missed the first time. The sonographer may ask you to walk around, drink cold water, or eat a snack to encourage the baby to shift positions during the scan itself.
How You Get Results
The sonographer captures the images, but they generally can’t give you an official interpretation during the scan. A radiologist or maternal-fetal medicine specialist reviews the images and sends a report to your OB or midwife. Some providers discuss preliminary findings with you the same day, while others call within a few days. If something concerning is found, you’ll typically hear sooner rather than later, and your provider may refer you for a more detailed ultrasound with a specialist.
If everything looks normal, the anatomy scan also serves as a reference point. Any ultrasounds later in pregnancy will compare your baby’s growth to the measurements taken at this visit, making it easier to spot changes in growth patterns over time.