First Trimester Anomaly Scan: What Happens at 11–13 Weeks?

The first trimester is an important stage of pregnancy when several early assessments may be recommended to monitor fetal development. A first trimester anomaly scan is a detailed ultrasound examination generally performed around 11–13 weeks of pregnancy. It can provide important information about the developing fetus and may be combined with other assessments depending on the pregnancy.

What Is a First Trimester Anomaly Scan?

A first trimester anomaly scan is a detailed ultrasound examination that looks at the fetus during the early stages of pregnancy. It allows a specialist to assess fetal development and examine specific anatomical features that can be evaluated at this stage.

The exact components of the examination can vary depending on the pregnancy and clinical requirements.

What Is NT Measurement?

NT (Nuchal Translucency) refers to the measurement of fluid at the back of the fetal neck. NT assessment is commonly performed during the 11–13-week period as part of first trimester screening.

An increased NT measurement can be associated with certain chromosomal or structural conditions, but it does not by itself confirm that a fetus has a particular condition. Results need to be interpreted alongside other screening information.

What Is NB Assessment?

NB (Nasal Bone) assessment involves examining the fetal nasal bone during the ultrasound. It may form part of a broader first trimester assessment alongside other ultrasound findings.

The findings are considered together rather than being interpreted as a standalone diagnosis.

What Is Doppler Assessment?

Depending on the examination and clinical indication, Doppler studies may also be performed. These can include assessment of blood flow in specific vessels, such as the Ductus Venosus (DV) and uterine arteries.

Doppler findings can provide additional information that may be useful when assessing certain pregnancy-related risks.

What Happens During the Scan?

The examination uses ultrasound imaging to obtain detailed views of the fetus. Measurements and observations are recorded according to the purpose of the examination.

In some situations, the position of the fetus may make certain views difficult to obtain. The specialist may therefore need additional time or recommend a repeat assessment when appropriate.

Why Is the 11–13 Week Period Important?

Certain fetal structures and measurements can be assessed particularly effectively during this stage of pregnancy. This is why the first trimester screening window is important for assessments such as NT measurement and early fetal anatomical evaluation.

The exact timing should be determined according to the pregnancy's gestational age and the advice of the treating healthcare professional.

What Happens After the Scan?

The results of the ultrasound should be interpreted by an appropriately qualified specialist. If a finding requires further evaluation, additional screening, diagnostic testing, or follow-up may be recommended.

A screening result does not necessarily mean that a condition is present. Further assessment may be required before any conclusions are reached.

Final Thoughts

A first trimester anomaly scan can provide valuable information about early fetal development and may include assessments such as NT, NB, DV, and uterine artery Doppler studies. However, the findings need to be considered as part of the overall pregnancy assessment.

If your doctor has recommended a first trimester ultrasound, discussing the purpose and timing of the examination with your healthcare professional can help you understand what the scan is intended to assess.

For specialised pregnancy imaging and fetal assessment, First Trimester Anomaly Scan services are available at Fetal Imaging Institute.