How do you make sense of pregnancy ultrasounds?
Dating, anatomy, growth: each ultrasound has a specific purpose — here's how to decode what's actually being checked.
The dating ultrasound, done between 11 and 14 weeks, measures the baby's length to confirm gestational age and the due date, often more precisely than a calculation based on your last period. It can also detect a multiple pregnancy and measure nuchal translucency as part of combined screening.
The anatomy ultrasound, done around 18 to 22 weeks, is longer and more detailed: it systematically checks the heart, brain, spine, kidneys, stomach, and limbs, along with the placenta's position and the amount of amniotic fluid. This is often when you can find out the baby's sex, if you'd like to know.
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Additional growth ultrasounds may be offered in the third trimester if certain factors call for it — multiple pregnancy, gestational diabetes, a concern about the baby's growth, or a placenta position worth watching. These measure the baby's estimated size and the amount of amniotic fluid at that stage.
It's worth keeping in mind that ultrasound remains an estimation tool, not a perfectly precise measurement: the estimated weight of the baby, for example, has a margin of error of around 10 to 15%. Your healthcare provider will always interpret results in the overall context of your pregnancy rather than relying on a single isolated number.
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This information is general and does not replace advice from your healthcare professional (doctor, midwife, nurse, pharmacist). Every situation is unique: always check with them before making a decision. In an emergency, call 911 or your local emergency services.
