What is a First Trimester Structural Survey Scan?
The First Trimester Structural Survey Scan is an advanced ultrasound examination performed between 11 and 13 weeks + 6 days of pregnancy. It evaluates the early development of fetal structures to detect major anomalies and confirm normal growth patterns.
Why is it done?
- To identify major structural anomalies early (e.g., neural tube defects, abdominal wall defects)
- To assess fetal growth parameters including crown-rump length (CRL)
- To evaluate the nuchal translucency (NT) measurement as a marker for chromosomal abnormalities
- To confirm number of fetuses and chorionicity in multiple pregnancies
- To provide early reassurance regarding fetal anatomy and development
When should I get it done?
The scan is ideally scheduled between 11 weeks and 13 weeks + 6 days of gestation. Performing it within this window ensures accurate anatomical assessment and risk stratification.
How is the scan performed?
- Transabdominal ultrasound with a full bladder provides optimal visualization
- The sonographer obtains standardized midsagittal and transverse views to assess anatomy
- CRL is measured for accurate dating, and NT is measured in a neutral fetal position
- Early assessment of nasal bone, ductus venosus flow, and tricuspid valve flow may be included
What does it show?
- Crown-rump length (CRL) and gestational dating
- Nuchal translucency (NT) thickness
- Presence and morphology of nasal bone
- Basic evaluation of brain, spine, abdominal wall, and limb buds
- Detection of multiple gestation and chorionicity
Benefits and Limitations
Benefits:
- Early detection of major fetal anomalies
- Accurate pregnancy dating
- Non-invasive and safe
Limitations:
- Cannot detect all anomalies (detailed anatomy scan at 18–22 weeks still required)
- Image clarity may be affected by fetal position or maternal factors
- Dependent on sonographer expertise
Frequently Asked Questions (FAQs)
Do I need any preparation for the scan?
Yes, having a moderately full bladder helps improve image quality.
Is the scan safe for my baby?
Yes. It uses ultrasound and has no known risks to the fetus.
How long does the scan take?
Approximately 20–30 minutes.
When will I receive the results?
Your sonographer will discuss findings immediately; a detailed report will follow.
What if an abnormality is detected?
You will be referred for further evaluation and genetic counseling if needed.