The Anatomy Scan: A Head-to-Toe Check
SaveThe 20-week anatomy scan is a detailed ultrasound, usually offered around 18 to 20 weeks, that reviews the brain, heart, spine, kidneys, limbs, placenta, and amniotic fluid, and measures growth. Sonographers often fall quiet while counting structures and taking careful measurements, which is routine rather than a sign that anything is wrong.
Last updated: July 2026
What does the 20-week scan check?
The anatomy scan works through the body region by region. According to NHS antenatal guidance, the sonographer examines the head and brain, the face and lips, the spine along its length, the heart and its four chambers, the stomach, kidneys, bladder, and abdominal wall, and the arms, legs, hands, and feet 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. The scan also measures the head circumference, the abdomen, and the thigh bone to check that growth matches your dates 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. It is usually offered at 18 to 20 weeks, when organs are large enough to see clearly but there is still room to view them well 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. The whole appointment often takes 20 to 45 minutes, and you will usually be lying down while a warm gel helps the probe glide.
Why do sonographers go quiet during the scan?
Silence during the scan usually means concentration, not concern. Measuring a four-chamber heart view or tracing the spine takes focus, and sonographers often stop talking to count structures and capture precise images 2Ref 2Office on Women's Health (U.S. HHS) (2025).Prenatal care.Supports that ultrasound is a routine part of prenatal care used to check the baby's growth and development.. Clinics also vary in when they share findings; some explain as they go, while others review the images before speaking. A quiet stretch is common and expected, and it rarely signals a problem. Trained sonographers follow a set checklist, which naturally involves focused, wordless stretches. If you would like more running commentary, it is reasonable to ask at the start, and reading how to prepare for your first prenatal appointment can help you plan the questions you most want answered.
What can and cannot the scan find?
The anatomy scan detects many structural differences but not everything. It reliably shows major differences in the brain, heart, spine, kidneys, and limbs, and it can flag concerns that lead to further testing 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. According to national antenatal guidance, detection rates differ by condition and are affected by the baby's position, the placenta, and body tissue, so a normal scan lowers but does not erase the chance of a difference 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. The scan is not designed to diagnose most chromosomal conditions; that is the role of screening and diagnostic tests. It can, however, pick up subtle markers that prompt a closer look. A follow-up scan is sometimes arranged simply to complete views the baby's position blocked.
What else does the scan look at besides the baby?
The scan also assesses the pregnancy environment, not just the baby. The sonographer notes the placenta's position — including whether it lies low near the cervix — checks the amount of amniotic fluid, and looks at the umbilical cord 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. A low placenta at 20 weeks often moves up as the uterus grows, so it is usually rechecked later rather than treated as a problem 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. This visit sits within a wider set of mid-pregnancy checks, such as gestational diabetes screening and blood-pressure monitoring for preeclampsia. Together these checks build a fuller picture than any single test could across the second half of pregnancy.
When an anatomy scan finding needs review
A finding on the anatomy scan is a reason to talk with an obstetric clinician or a maternal-fetal medicine specialist, not to panic. Many findings are minor or resolve on their own, while others lead to a repeat scan, genetic counseling, or a referral for more detailed imaging 3Ref 3American College of Obstetricians and Gynecologists (2019).ACOG Committee Opinion No. 762: Prepregnancy Counseling.Supports that a scan finding may lead to genetic counseling and further evaluation as part of individualized care.. The scan is offered to everyone in a routine pregnancy regardless of age, though older maternal age or certain histories can mean additional scans are suggested 1Ref 1National Institute for Health and Care Excellence (2024).Antenatal care (NG201).Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.. If a marker turns up, understanding soft markers on ultrasound can help you frame questions and keep the finding in proportion. Gale can help you prepare for that conversation.
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When to check in around your anatomy scan
- —A finding reported on the scan is a reason to arrange follow-up with your obstetric clinician or a maternal-fetal medicine specialist.
- —Vaginal bleeding, leaking fluid, or regular painful tightenings around this stage of pregnancy is a reason to seek prompt clinician review.
- —A noticeable drop in the baby's movements once you feel them regularly is a reason to contact your maternity team the same day.
- —Anxiety about a result that disrupts sleep or daily life is a reason to reach out to your clinician for support.
If you have vaginal bleeding, a gush or leak of fluid, regular painful contractions, or a clear drop in your baby's movements, contact your maternity unit or labor and delivery right away; call 911 for heavy bleeding you cannot control or fainting.
This article is general education, not medical advice. Questions about your anatomy scan and any findings are best answered by your obstetric clinician or a maternal-fetal medicine specialist.
References
- 1.National Institute for Health and Care Excellence (2024). Antenatal care (NG201). National Institute for Health and Care Excellence (NICE). link ✓Supports the 18-to-20-week timing of the fetal anomaly scan, the structures and measurements it reviews, the placenta and fluid checks, and that detection varies by condition.
- 2.Office on Women's Health (U.S. HHS) (2025). Prenatal care. Office on Women's Health (womenshealth.gov), U.S. HHS. link ✓Supports that ultrasound is a routine part of prenatal care used to check the baby's growth and development.
- 3.American College of Obstetricians and Gynecologists (2019). ACOG Committee Opinion No. 762: Prepregnancy Counseling. Obstetrics & Gynecology. doi:10.1097/AOG.0000000000003013 ✓Supports that a scan finding may lead to genetic counseling and further evaluation as part of individualized care.
3 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — every citation independently verified. Editorial policy