The 20-week anatomy scan, also known as the fetal anatomy scan or mid-trimester ultrasound, is one of the most important routine prenatal screenings during pregnancy. For intended parents pursuing surrogacy, this scan offers a critical look at the developing baby’s health and structural development.
This article will walk you through what this ultrasound examines, why it matters, what it can and cannot detect—and how to interpret the results. We’ll also address common misconceptions and key considerations for intended parents working with a gestational carrier.
🔍 What Is the Fetal Anatomy Scan?
The fetal anatomy scan is a detailed ultrasound performed between 18 and 22 weeks of pregnancy. Its primary goal is to examine the fetus’s anatomy and physical development, identifying any major structural abnormalities before birth. If you’re unsure about how far along you are, you can use our Due Date Calculator to estimate your current stage of pregnancy.
During this exam, a trained sonographer (ultrasound technician or physician) uses ultrasound technology to capture real-time images of the fetus in the womb. They evaluate growth metrics and carefully examine each major organ and limb.
For surrogacy journeys, the scan is typically performed at the clinic or hospital where the gestational carrier receives her prenatal care. Intended parents often receive a detailed written report.
⏳ When Is It Done and Why?
The scan is ideally performed between 18 and 22 weeks of gestation, when the baby’s organs are fully formed and visible via ultrasound. Scanning earlier may miss some abnormalities, while later scans may reduce the options available for further diagnostic testing or reproductive choices.
🔬 Professional guidance: The American College of Obstetricians and Gynecologists (ACOG) recommends a second-trimester detailed fetal anatomical ultrasound for all pregnancies between 18–22 weeks. Source: ACOG Committee Opinion No. 700
🔍 What Is Checked During the Fetal Anatomy Scan?
The anatomy scan is a head-to-toe evaluation of the fetus. Commonly examined areas include:
- Brain, skull, and spine: checking for neural tube defects, ventriculomegaly, or missing brain structures
- Face: detecting cleft lip or other facial asymmetries
- Heart: evaluating chambers, valves, and rhythm (for major congenital heart defects)
- Lungs and chest wall
- Stomach and intestines
- Kidneys and bladder
- Limbs and digits: ensuring normal number and development
- Genitalia: identifying fetal sex (if desired)
- Umbilical cord: confirming proper blood flow and cord insertion
- Placenta: checking position (e.g., placenta previa) and maturity
- Amniotic fluid levels
- Cervix and uterine anatomy
The sonographer will take multiple measurements and compare them to gestational age standards. If the baby’s growth is within 10–14 days of the expected due date, it’s typically considered normal.
🖥️ How Is the Fetal Anatomy Scan Performed?
The anatomy scan is a non-invasive procedure using abdominal ultrasound. The gestational carrier lies on an exam table while a technician applies a special gel on her abdomen and moves a handheld probe to generate images.
The procedure usually takes 30 to 60 minutes, depending on fetal position and image clarity. If the baby is not in an optimal position, the technician may ask the patient to shift positions—or even schedule a follow-up scan to complete the evaluation.
📋 Understanding the Results
After the scan, the medical team reviews findings and provides a report. Results typically fall into three categories:
- Normal anatomy: No structural concerns are found.
- Inconclusive: Some structures couldn’t be seen clearly—often due to fetal position. A repeat scan may be scheduled.
- Abnormal finding: A concern is noted that may require further investigation.
Follow-up steps may include:
- Detailed level II ultrasound (targeted scan)
- Fetal echocardiogram (for heart concerns)
- Amniocentesis (for genetic or chromosomal analysis)
- Fetal MRI (for complex brain or spine issues)
- Genetic counseling
- Consulting with your support system (agency, therapist) for emotional guidance.
💬 A Note on “Soft Markers”
Some findings are considered “soft markers”—minor variations (like an echogenic bowel or choroid plexus cysts) that are not abnormalities themselves but may be associated with a slightly increased risk for other conditions. Many soft markers resolve on their own or are confirmed to be harmless variants. It’s important not to panic and to follow your care team’s recommendations.
⚠️ Common Misconceptions About the Fetal Anatomy Scan
1. It’s not a perfect test.
While the scan is highly effective, it cannot catch every abnormality. Detection rates vary, but on average, the scan identifies over half of major structural issues. However, some conditions—such as certain genetic syndromes (like Down syndrome, which has markers but no definitive sign), metabolic disorders, or very minor defects—are not always visible on ultrasound. Additionally, fetal position can obscure certain structures, limiting the evaluation.
2. Abnormal findings don’t always mean serious problems.
Not every abnormality is life-threatening. Some findings turn out to be minor variants, and others resolve naturally. A single “soft marker” often requires no intervention but may prompt closer monitoring or additional screening.
3. Timing matters.
Because legal restrictions on pregnancy termination differ by state—and many states limit abortion after 24 weeks—it’s best to complete the scan by 22 weeks. This ensures there is time to receive results, follow up with further testing if needed, and consider all available options.
4. Always ask for the written report.
Some technicians may verbally report findings to the gestational carrier, but intended parents should request the official report for full transparency. Medical terminology can be confusing, and written documentation ensures accuracy in interpretation.
🔗 How the Fetal Anatomy Scan Relates to PGT-A, NIPT, and NT Scan
- PGT-A Screens embryos before transfer for chromosomal abnormalities, but cannot detect structural defects. The anatomy scan complements it by evaluating physical development.
- NIPT A non-invasive blood test that assesses chromosomal risks. It does not replace the anatomy scan, which provides detailed organ assessment.
- NT Scan Done at 11–13 weeks, it measures fluid behind the fetal neck. While useful for early risk prediction, it cannot substitute the 20-week scan for anatomical detail.
🧠 Key Takeaways for Intended Parents
- Schedule the fetal anatomy scan between 18–22 weeks.
- Ask for the written report, not just verbal communication.
- Remember: normal scans are reassuring, but not absolute guarantees.
- If an abnormality is found, don’t panic—seek a second opinion or further testing.
- Consult with a genetic counselor if recommended by your care team.
❓ FAQs About the Fetal Anatomy Scan
1. Can we attend the anatomy scan if we’re using a surrogate?
If you wish to attend the scan in person, please discuss your preferences with your agency early in the process. The agency will do its best to coordinate, but ultimately, whether you can attend depends on your surrogate’s OB provider. The doctor will make the final decision based on clinic policy, medical considerations, and patient comfort.
2. Does the anatomy scan detect Down syndrome or other genetic conditions?
Not directly. It can identify some physical markers associated with these conditions, but diagnostic tests like amniocentesis are required for a definitive diagnosis of genetic abnormalities.
3. What happens if something abnormal is found?
Your OB may refer you to a Maternal-Fetal Medicine (MFM) specialist for a Level II ultrasound, fetal echocardiogram, or amniocentesis. In some cases, additional monitoring is all that’s needed.
4. Is it safe for the baby?
Yes. Ultrasound is a non-invasive, widely used technology with no known risks to the fetus when performed by trained professionals.
5. Can the scan tell us the baby’s gender?
In most cases, yes—if the baby is in a position that allows clear visibility of the genitalia.
6. Can the scan be done too early or too late?
Before 18 weeks, organs may not be fully developed or visible. After 22 weeks, it may be too late for certain follow-up decisions if serious issues are detected.
7. How accurate is the scan?
Accuracy depends on gestational age, technician skill, equipment quality, and fetal position. Most major structural issues can be detected, but not all.
8. Do we need additional scans later in pregnancy?
Possibly. Some pregnancies may require follow-up growth scans in the third trimester or specialized imaging based on earlier findings.
📚 References
- American College of Obstetricians and Gynecologists. (2017). Methods for Estimating the Due Date. ACOG Committee Opinion No. 700. (Reaffirmed 2020). Link via PubMed
- Dashe, J. S., & Twickler, D. M. (2023). Obstetric Ultrasound: Fetal Aneuploidy and Congenital Anomalies. In StatPearls. StatPearls Publishing. (Cites SMFM guidelines). Link via NCBI
Medically reviewed by Dr. Diana LeBlanc, MD – Reproductive Endocrinologist at Hanabusa IVF
