NT Scan Results Explained — Understanding Your Report

The nuchal translucency (NT) scan at 11–13+6 weeks is a key first-trimester screening test for chromosomal abnormalities. This page explains exactly what the scan measures, what the report means, and what to do with the results.

1. What the NT scan is

Ultrasound performed between 11 weeks 0 days and 13 weeks 6 days. Measures the fluid-filled space at the back of the fetal neck (nuchal translucency). Increased NT thickness is associated with chromosomal abnormalities (Down syndrome, Edwards, Patau) and structural anomalies. Performed by ISUOG-trained sonographers.

2. What is measured

Crown-rump length (CRL) — confirms gestational age. Nuchal translucency thickness, the screening measurement. Nasal bone presence/absence. Heart rate. Major structural anomalies visible at this stage. The scan also confirms viability, number of fetuses, and chorionicity in multiple pregnancies.

3. Combined first-trimester screening

NT measurement is combined with maternal age and two blood biomarkers — PAPP-A and free beta-hCG. The combined risk calculation gives an individualised risk for trisomy 21, 18 and 13. Detection rate approximately 85–90% for Down syndrome with 5% false positive.

4. Interpreting the result

Low risk: result reassuring; routine antenatal care continues. Increased risk: depending on threshold (commonly 1 in 250 or 1 in 100), further testing offered — NIPT (non-invasive prenatal test) or diagnostic test (CVS at 11–14 weeks, amniocentesis from 15 weeks). Increased NT itself warrants extra fetal echo at 20 weeks even if karyotype normal.

5. NIPT — the next step

Non-invasive prenatal testing analyses fetal DNA in maternal blood. Detects trisomy 21, 18, 13, sex chromosome abnormalities and selected microdeletions. Highly accurate (over 99% for Down syndrome) but still a screening test, positive results need confirmation by CVS or amnio. Available from 10 weeks. Cost variable across India.

6. Diagnostic testing — CVS and amniocentesis

Chorionic villus sampling (CVS) at 11–14 weeks, takes placental tissue. Amniocentesis from 15 weeks, takes amniotic fluid. Both provide definitive chromosomal diagnosis. Procedure-related miscarriage risk: under 0.5% in experienced hands. Reserved for high-risk screening or specific indications.

7. What if NT is increased but karyotype is normal

Increased NT (over 3.5 mm) with normal karyotype is associated with congenital heart defects. Detailed fetal echocardiography at 18–22 weeks is recommended. Most pregnancies with isolated increased NT and normal karyotype proceed normally with healthy babies. Surveillance is the prudent approach.

8. What if findings are abnormal

Genetic counselling. Discussion of management options including continuation of pregnancy with planning, termination if legally and personally acceptable, or further testing. Decisions are deeply personal; specialists provide information, not directives. Support through this period is essential.

9. After your NT scan: what the next step depends on

The NT scan and combined first-trimester screening give a risk estimate, not a diagnosis. What happens next depends on that estimate. If your combined result is low risk, routine antenatal care continues and the next major check is the mid-pregnancy anomaly (TIFFA) scan at 18–22 weeks. If the result is increased risk, two broad paths are usually discussed.

The first is a more accurate screening test. NIPT (non-invasive prenatal testing) analyses fragments of placental DNA in the mother’s blood and detects over 99% of Down syndrome with a far lower false-positive rate than the double marker or combined test. The older double marker test is the first-trimester blood component (PAPP-A and free beta-hCG) of combined screening; NIPT is more accurate and is widely available in Ahmedabad. Our guide to NIPT versus the double marker test explains how to choose. The second path, offered when risk is high or a definitive answer is needed, is a diagnostic test (CVS or amniocentesis) — the only way to confirm a chromosomal condition. A “high-risk” screening result does not mean the baby is affected; most babies after an increased-risk screen are healthy, which is exactly why confirmation matters before any decision is made.

10. What a normal NT result does — and does not — tell you

A reassuring NT result meaningfully lowers the chance of the common chromosomal conditions, but it has limits worth understanding. It is a screening test for chromosomal risk, not a guarantee, and it does not replace the anomaly scan at 18–22 weeks, the detailed fetal medicine examination of the baby’s structure. A normal NT also does not assess every genetic condition — only those covered by the specific test performed. This is why screening is offered as a structured prenatal screening pathway across the pregnancy rather than a single test, and why an isolated increased NT with a normal karyotype still prompts a dedicated fetal heart scan later in pregnancy.

Sources and further reading

This page reflects current international guidance on first-trimester screening:

• ISUOG Practice Guidelines (updated 2023): performance of the 11–14-week ultrasound scan.
• FIGO guidance on best practice in prenatal screening for fetal aneuploidy.
• NICE Antenatal Care (NG201) and the NHS Fetal Anomaly Screening Programme.

Last updated: 6 July 2026 · Reviewed by the fetal medicine team, Balaji Horizon Women’s Hospital. Educational information only; it does not replace individual medical advice.