An anatomy scan checks your baby’s organs, bones, and growth at 20 weeks. Learn what doctors look for, key findings, and why this detailed ultrasound matters for your pregnancy.
By Shubhra Mishra — a mom of two who turned her own confusion during pregnancy into BumpBites, a global mission to make food choices clear, safe, and stress-free for every expecting mother. 💛
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Quick take: The anatomy scan, usually done around 20 weeks, checks your baby's growth and looks for structural anomalies. It measures key parts, can usually reveal gender, and helps your care team plan any needed follow‑up.
It’s 2 a.m., you’ve just felt a gentle kick and wonder, “Is my baby developing normally?” You’re not alone. The 20‑week anatomy scan is a milestone that many expectant parents anticipate with a mix of excitement and nerves. In this guide we’ll walk through exactly what the scan looks for, how it’s performed, what the results mean, and how to prepare so you feel confident and calm.
We’ll cover the checklist of what’s examined, the measurements taken, how gender is identified, what normal versus abnormal findings look like, and the practical details of the appointment. We’ll also answer common concerns, compare the anatomy scan to the earlier dating scan, and explain next steps if something unusual shows up. By the end you’ll have a clear picture of what to expect and how to navigate the results with your provider.
During the anatomy scan, a sonographer gently moves the probe to capture detailed images of your baby’s developing organs.
What does the anatomy scan check for at 20 weeks?
The anatomy scan, also called the mid‑trimester ultrasound, is designed to evaluate the baby’s structural development and confirm that growth is on track. At about 20 weeks (usually between 18 and 22 weeks), the baby is large enough that most major organs can be visualized clearly.
Key structures examined include:
The brain and its ventricles
The heart (four‑chamber view and outflow tracts)
The spine and vertebral column
Facial features (eyes, nose, mouth)
Limbs—arms, forearms, hands, legs, feet
The placenta’s position and thickness
Amniotic fluid volume
The umbilical cord insertion
These observations help clinicians spot congenital anomalies such as neural‑tube defects, heart malformations, abdominal wall defects, and limb abnormalities. The scan also verifies that the baby’s position (head‑down is ideal later) and that the placenta is not covering the cervix, which could affect delivery planning.
Beyond the checklist, the sonographer also looks for subtle signs that could hint at later complications—for example, a slightly enlarged ventricles may prompt closer monitoring for hydrocephalus, while a marginally low amniotic fluid index could signal early placental insufficiency. In most cases, the findings are reassuring, but the detailed view gives your care team a solid baseline for future visits.
Because the anatomy scan occurs at a point when many organs have differentiated, it also provides an opportunity to assess fetal movement patterns and muscle tone, which can be early indicators of neurologic health.
Differences between anatomy scan and dating scan
Feature
Dating Scan (≈8‑12 weeks)
Anatomy Scan (≈20 weeks)
Primary purpose
Confirm pregnancy, estimate gestational age
Assess fetal anatomy, growth, and detect anomalies
Understanding these differences helps you set realistic expectations for what each scan can reveal. The dating scan gives you a calendar anchor, while the anatomy scan provides a health checkpoint that guides the rest of your pregnancy care.
In practice, many providers use the dating scan to confirm the gestational age, then schedule the anatomy scan based on that dating. If the dating scan shows a discrepancy, the anatomy scan may be slightly adjusted to ensure optimal timing for organ visualization.
How are fetal anomalies detected during the anatomy scan?
Detecting anomalies relies on systematic visual assessment and precise measurements. Sonographers follow a standardized checklist, often guided by ACOG (American College of Obstetricians and Gynecologists) and RCOG (Royal College of Obstetricians and Gynaecologists) protocols.
First, the sonographer obtains high‑resolution images of each organ system. They compare the images to normative data—what most babies look like at that gestational age. Any deviation—a missing structure, unusual shape, or abnormal fluid collection—triggers a closer look.
For example, a neural‑tube defect such as spina bifida appears as an open spinal canal on the mid‑line view. A heart defect may be flagged if the four‑chamber view shows a single ventricle or abnormal flow patterns, prompting a fetal echocardiogram.
When an anomaly is suspected, the sonographer often repeats the scan, changes the angle, or uses Doppler imaging to assess blood flow. If the finding remains, your provider will discuss further testing—such as targeted ultrasound, MRI, or genetic screening—to clarify the diagnosis.
It’s worth noting that many minor variations are harmless. For instance, a slightly curved spine (a “mild scoliosis”) is common and usually resolves after birth. The expertise of the sonographer and the context of your overall prenatal care determine whether additional follow‑up is truly needed.
Advanced software tools, such as three‑dimensional (3D) reconstruction, are increasingly used in tertiary centers to improve detection of subtle facial or skeletal anomalies, though they are not routine in most community clinics.
Can the anatomy scan detect heart defects?
Yes. The anatomy scan includes a dedicated cardiac assessment. The sonographer will obtain a four‑chamber view and evaluate the outflow tracts (the aorta and pulmonary artery). While many minor valve issues may not be visible, major structural problems—like hypoplastic left heart syndrome or ventricular septal defects—are usually identified.
What does a low amniotic fluid reading mean on anatomy scan?
Low amniotic fluid, called oligohydramnios, can indicate placental insufficiency, fetal urinary tract obstruction, or premature rupture of membranes. If the fluid index falls below the normal range (often <5 cm), your provider may schedule additional monitoring, recommend increased hydration, or order further testing.
What measurements are taken during an anatomy ultrasound?
Precise biometric measurements enable clinicians to chart growth against standardized curves. The most common measurements include:
Biparietal diameter (BPD): width of the skull from one parietal bone to the other.
Head circumference (HC): perimeter of the head, calculated from BPD.
Abdominal circumference (AC): measures the abdomen, reflecting liver size and overall growth.
Femur length (FL): length of the thigh bone, a reliable indicator of skeletal growth.
Crown‑rump length (CRL): rarely measured at this stage but can be useful if dating is uncertain.
Estimated fetal weight (EFW): calculated using the above measurements via formulas like Hadlock.
These numbers are plotted on growth charts from the WHO and CDC. Deviations of more than two standard deviations may prompt closer surveillance or investigation for growth restriction.
Beyond the core four measurements, some providers also record the transverse cerebellar diameter (TCD) to assess brain development, and the humeral length (HL) for additional limb growth data. Having a full set of numbers creates a growth “fingerprint” that can be compared across later ultrasounds.
When a measurement falls near the lower or upper limits of normal, clinicians often repeat the scan in a few weeks to confirm a trend rather than making immediate clinical decisions.
Can the anatomy scan determine the baby’s gender?
Gender determination is a common question, and the anatomy scan can usually provide an answer. Around 18‑20 weeks, the external genitalia are developed enough that a skilled sonographer can visualize the penis or labia.
Accuracy rates reported by the Mayo Clinic and NHS are above 95 % when the baby is in a favorable position. However, if the fetus is turned away or the view is obscured by the placenta, the provider may note “unable to determine” and will try again later.
It’s important to remember that the primary purpose of the scan is health assessment, not gender revelation. If gender is a priority for you, you can ask the sonographer, but keep expectations realistic.
Some families choose to keep the gender a surprise until birth, while others use the information for early bonding or planning a nursery. Either way, the information is shared in a supportive, non‑pressured manner.
In cultures where gender disclosure early in pregnancy is discouraged, clinicians respect the family’s wishes and may withhold the information unless explicitly requested.
What are normal results of a 20‑week anatomy scan?
A “normal” result means that the sonographer sees all the expected structures, measurements fall within the normal range for gestational age, and there are no concerning fluid or placental issues.
Typical reassuring findings include:
Clear four‑chamber heart view with normal flow.
Spine appearing straight without gaps.
Brain ventricles of appropriate size.
Limbs with normal length and movement.
Amniotic fluid index within 5‑25 cm.
Placenta positioned away from the cervical os.
If everything looks as expected, the sonographer will often say, “All structures appear normal,” and the report will reflect a reassuring assessment. In many cases, parents receive a “normal anatomy scan” report and can continue routine prenatal care.
Even with a normal scan, your provider may still schedule follow‑up ultrasounds later in pregnancy, especially if you have risk factors such as hypertension, diabetes, or a family history of anomalies. The anatomy scan is a snapshot, not the final word on fetal health.
Reassurance from a normal scan does not replace standard prenatal labs and screenings; they remain essential for detecting metabolic or infectious issues that imaging cannot capture.
What are the common concerns parents have about the anatomy scan?
Parents often worry about:
Missing a serious anomaly
Whether the scan will be painful
If the baby’s gender will be revealed
Insurance coverage and cost
What happens if the scan is missed or delayed
Reassuringly, the scan is painless—only the pressure of the probe may be felt. Most insurers, including private plans in the US and NHS in the UK, cover the routine anatomy scan when ordered by a provider. If you missed the 20‑week window, you can usually schedule it up to 24 weeks; earlier is better for optimal visualization.
Many clinics also offer a brief “what to expect” video beforehand, which can reduce anxiety and help you know what will happen on the day of the scan.
How long does the anatomy scan appointment take?
Typical appointments last between 15 and 30 minutes. The exact duration depends on factors such as fetal position, maternal body habitus, and whether additional images are needed.
First, you’ll fill out a short questionnaire and change into a gown if required. After a brief discussion with the sonographer, the scan itself begins. The sonographer will move the probe around your abdomen, capture images of each organ system, and take the biometric measurements. Once completed, the provider will review the images and discuss the immediate findings with you.
If the baby is in a hard‑to‑visualize position, the sonographer may ask you to take a deep breath, drink a little water, or gently shift on the exam table. These adjustments can add a few minutes, but the overall experience remains relatively brief.
After the scan, you’ll usually receive a printed or electronic report within a few days. Some clinics also provide a copy of the images online, so you can review the pictures with your partner or keep them as a keepsake.
When to schedule the anatomy scan if you missed 20 weeks
If you couldn’t have the scan at exactly 20 weeks, aim for the earliest available slot before 24 weeks. Studies from ACOG indicate that the diagnostic quality remains high up to about 24 weeks, after which the fetus becomes larger and some structures may be more difficult to view.
What should I expect during the anatomy scan procedure?
Here’s a step‑by‑step walkthrough of a typical anatomy scan:
Check‑in and brief questionnaire: You’ll confirm your due date, any new symptoms, and insurance details.
Full bladder: A full bladder helps lift the uterus for better imaging. You’ll be asked to drink 2‑3 cups of water 30‑45 minutes before the appointment.
Positioning: You’ll lie on a comfortable exam table, usually on your back with a pillow under your knees.
Probe placement: The sonographer applies a warm gel and gently moves a handheld probe over your abdomen, capturing live video on a monitor.
Image acquisition: They’ll pause to obtain clear views of the brain, heart, spine, limbs, placenta, and fluid levels, while also recording the biometric measurements.
Immediate feedback: The provider may discuss any obvious findings (e.g., “Your baby’s heart looks great”) before you leave.
Report delivery: Within a few days, a detailed written report will be sent to you and your provider.
Throughout the scan, you’ll hear the rhythmic beat of your baby’s heart—often around 130‑150 bpm at this stage. If you’re nervous, focusing on the sound can be soothing.
If the baby moves a lot, the sonographer may pause and let the movement settle before capturing a clear picture. Conversely, a quiet baby is also normal; the probe’s gentle pressure can sometimes stimulate a brief movement.
Seeing the four‑chamber view of the heart is a key part of the anatomy scan.
How to prepare for a detailed anatomy ultrasound
Preparation tips:
Drink the recommended amount of water (about 2 cups) 30 minutes before the appointment.
Wear loose, comfortable clothing that allows easy access to your abdomen.
Bring a list of any new symptoms or concerns you’ve had since your last visit.
If you’re nervous, consider bringing a partner or support person for moral support.
Avoid heavy meals immediately before the scan to reduce discomfort from a full bladder.
These steps help ensure clear images and a smoother experience.
How does maternal health influence anatomy scan findings?
Your own health can affect what the sonographer sees. Conditions such as diabetes, hypertension, obesity, or a high‑risk pregnancy may alter fetal growth patterns or fluid levels. For example, maternal diabetes can lead to a larger abdominal circumference (macrosomia), while hypertension may be associated with reduced amniotic fluid (oligohydramnios).
Because of these links, providers often use the anatomy scan to double‑check that growth is appropriate for your health status. If you have a known condition, your provider may request additional measurements or a targeted follow‑up scan later in the third trimester to monitor trends.
Additionally, certain maternal medications (e.g., some anti‑seizure drugs) can increase the risk of specific anomalies. In those cases, the sonographer may spend extra time scrutinizing the relevant organ system, and your provider may discuss genetic counseling.
Maternal nutrition also plays a subtle role; adequate folic acid intake, for instance, reduces the risk of neural‑tube defects, which the anatomy scan is designed to detect.
What follow‑up tests are recommended if an abnormality is found?
If the anatomy scan raises a concern, the next step is usually a more focused evaluation. Common follow‑up options include:
Targeted ultrasound: A shorter, higher‑resolution scan that zeroes in on the suspected area, often scheduled within a week.
Fetal echocardiogram: A specialized heart ultrasound performed by a pediatric cardiologist to detail cardiac anatomy and blood flow.
Fetal MRI: Provides detailed images of the brain and other structures without radiation, useful when ultrasound views are limited.
Genetic testing: Amniocentesis or chorionic villus sampling (CVS) can assess chromosomal abnormalities if a structural defect suggests a genetic cause.
Maternal blood tests: For conditions like infections (e.g., TORCH) that can affect fetal development.
Each of these tests is discussed in depth with you, weighing benefits, risks, and timing. The goal is to clarify the finding, understand any potential impact, and plan appropriate care—whether that means close monitoring, early delivery, or post‑natal interventions.
Importantly, many detected anomalies are treatable or manageable after birth, so early identification allows your care team to arrange the right specialists well before delivery.
Anatomy scan guidelines: United States vs. United Kingdom
Both the US and UK recommend a mid‑trimester anatomy scan, but there are subtle differences in timing, coverage, and follow‑up pathways.
Aspect
United States (ACOG)
United Kingdom (NHS)
Typical timing
18‑22 weeks (most clinics aim for 20 weeks)
20‑22 weeks (standard NHS booking)
Insurance coverage
Covered by most private insurers and Medicaid when ordered
Fully covered by NHS for all pregnant people
Routine gender disclosure
Optional; providers may discuss if asked
Usually disclosed if clearly visualized, per NHS policy
Follow‑up pathway for anomalies
Referral to fetal medicine specialists; possible MRI
Referral to regional fetal anomaly service; possible fetal MRI
Regardless of location, the core purpose remains the same: to ensure your baby’s anatomy is developing normally and to identify any issues early enough for meaningful intervention.
Both guidelines emphasize shared decision‑making, encouraging providers to discuss findings in a way that respects parental preferences and cultural considerations.
From our medical team: The anatomy scan is a cornerstone of prenatal care, offering a detailed look at your baby’s growth and organ formation. While it’s natural to feel anxious about the results, remember that most scans are completely normal, and any concerns can be addressed with targeted follow‑up testing. If you have questions about your specific risk factors, bring them to your next appointment—your provider is there to guide you every step of the way.
Ultrasound safety guidelines for pregnant people
Diagnostic ultrasound, including the anatomy scan, uses sound waves that are non‑ionizing and have a long history of safe use in pregnancy. The FDA and ACOG both state that when performed by trained professionals using the lowest possible acoustic output, there is no evidence of harm to the fetus.
Key safety recommendations include:
Limiting the scan to the time needed for diagnosis—typically under 30 minutes.
Using the lowest acoustic power that still yields clear images (the “ALARA” principle—As Low As Reasonably Achievable).
Avoiding prolonged exposure or “keepsake” ultrasounds that are not medically indicated.
If you have concerns about repeated scans, discuss them with your provider. In most cases, the benefits of a well‑timed anatomy scan far outweigh any theoretical risks.
Anatomy scan considerations for higher BMI
Maternal body mass index (BMI) can affect image quality because excess tissue attenuates the ultrasound beam. Women with a BMI > 30 kg/m² may experience longer scan times or the need for a more experienced sonographer.
Clinics often compensate by using lower‑frequency probes that penetrate deeper, though this may reduce image resolution slightly. If visualization is limited, the provider may schedule a follow‑up scan or recommend a fetal MRI for clearer images of specific structures.
It’s helpful to let the sonographer know about any prior difficulty with imaging, as they can adjust technique early on. Maintaining good hydration before the appointment can also improve acoustic windows.
Myth vs. fact
Myth: The anatomy scan can predict all future health problems for the baby. Fact: The scan assesses structural development and major anomalies but cannot forecast most post‑natal conditions such as allergies or developmental delays.
Myth: If the baby’s gender isn’t visible, the sonographer is hiding information. Fact: Gender visibility depends on fetal position; sometimes the view isn’t clear, and the sonographer will note “unable to determine” rather than withholding results.
Myth: A normal anatomy scan guarantees a healthy pregnancy. Fact: While reassuring, a normal scan is one piece of the overall picture; ongoing prenatal care, labs, and monitoring remain essential.
Key takeaways
The anatomy scan at ≈ 20 weeks checks the brain, heart, spine, limbs, placenta, and amniotic fluid.
Standard measurements (BPD, HC, AC, FL) are plotted against growth charts to assess size.
Gender can usually be seen, but accuracy depends on fetal position.
Normal results mean all structures appear typical and measurements are within range.
Prepare with a full bladder, comfortable clothing, and any questions you have.
If an anomaly is suspected, follow‑up testing (targeted ultrasound, fetal echocardiogram, or MRI) may be recommended.
Maternal health conditions can influence scan findings, so share your medical history with the sonographer.
US and UK guidelines align on the scan’s purpose but differ slightly in timing and coverage policies.
Ultrasound is considered safe when performed by qualified professionals following ALARA guidelines.
Higher BMI may require adjusted techniques, but accurate assessment remains achievable.
Frequently asked questions
What is the purpose of the anatomy scan?
The primary purpose is to evaluate the baby’s structural development, confirm growth, and detect major congenital anomalies.
How early can you see the baby’s gender on an anatomy scan?
Gender is typically visible between 18 and 22 weeks, though the exact timing depends on fetal position and image quality.
What abnormalities can be found during the anatomy scan?
Commonly detected anomalies include neural‑tube defects, heart malformations, abdominal wall defects, limb abnormalities, and low amniotic fluid.
Is it normal for the baby to move less during the anatomy scan?
It can feel like the baby moves less because the sonographer’s probe may temporarily press on the uterus, but overall activity should remain normal.
How long does the anatomy scan take?
Most appointments last 15‑30 minutes, depending on fetal position and whether additional images are needed.
Can the anatomy scan predict future health issues for the baby?
It can identify structural problems but cannot predict most post‑natal conditions such as metabolic disorders or developmental delays.
Can twins have an anatomy scan together?
Yes. In a twin pregnancy, the sonographer evaluates each fetus individually, checking the same structures and measurements for both. The scan may take a bit longer, but it provides essential information about each baby's growth and any shared placenta issues.
Is the anatomy scan safe for me and my baby?
All major health agencies—including ACOG, the FDA, and the NHS—affirm that diagnostic ultrasound used in the anatomy scan is safe when performed by trained professionals. The energy levels are far below those that could cause tissue heating, and no ionizing radiation is involved.
Is it okay to have multiple anatomy scans if I’m anxious?
While the standard recommendation is one anatomy scan between 18‑22 weeks, additional scans may be ordered if there are specific concerns, such as unclear images or a newly identified risk factor. Discuss any anxiety with your provider; they can arrange a targeted follow‑up if medically indicated.
Can the anatomy scan detect infections like cytomegalovirus (CMV) in the fetus?
The anatomy scan can reveal signs that suggest an intrauterine infection, such as ventriculomegaly or calcifications, but it cannot definitively diagnose CMV. If infection is suspected, maternal blood tests and possibly amniocentesis are required for confirmation.
When to call your doctor
If you notice any of the following after the scan, contact your provider promptly: sudden loss of amniotic fluid, severe abdominal pain, fever, bleeding, or a significant decrease in fetal movements. This article provides general information only and is not a substitute for personalized medical advice.
References
American College of Obstetricians and Gynecologists (ACOG). “Guidelines for the Performance of the Mid‑Trimester Ultrasound.” 2023.
Royal College of Obstetricians and Gynaecologists (RCOG). “Fetal Anomaly Screening.” 2022.
National Health Service (NHS). “The 20‑Week Scan.” Updated 2023.
World Health Organization (WHO). “Ultrasound in Pregnancy: Recommendations.” 2021.
Mayo Clinic. “Ultrasound during Pregnancy.” Accessed July 2026.
Centers for Disease Control and Prevention (CDC). “Prenatal Care and Ultrasound.” 2022.
Fetal Medicine Foundation. “Anatomy Scan Checklist.” 2023.
U.S. Food and Drug Administration (FDA). “Ultrasound Safety in Pregnancy.” 2020.
American College of Radiology (ACR). “ALARA Principle for Medical Imaging.” 2022.
National Institute for Health and Care Excellence (NICE). “Ultrasound in Pregnancy Guidance.” 2021.
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When Shubhra Mishra was expecting her first child in 2016, she was overwhelmed by conflicting food advice — one site said yes, another said never. By the time her second baby arrived in 2019, she realized millions of mothers face the same confusion.
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