Nuchal Translucency
Calculate fetal nuchal translucency percentile from CRL and NT ultrasound measurements. Free online NT screening tool with risk classification and comparison charts.
About This Calculator
The Nuchal Translucency (NT) Calculator helps expectant parents and healthcare professionals assess fetal nuchal translucency measurements from first-trimester ultrasound scans. By entering the crown-rump length (CRL) and the measured NT thickness, this calculator determines the NT percentile, compares the measured value against the expected NT, and provides a risk classification. NT screening is performed between 11 and 14 weeks of pregnancy and is a key component of first-trimester aneuploidy screening.
The expected NT is calculated using the formula Expected NT = 0.437 + (0.01969 × CRL), derived from large population studies. The measured NT is then compared against validated percentile reference charts (5th, 25th, 50th, 75th, and 95th percentiles) for the given CRL value. NT measurements below the 95th percentile are considered within the normal range, while measurements at or above the 95th percentile indicate elevated risk for chromosomal abnormalities such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), and Turner syndrome.
Regional Notes
India: First-trimester NT screening is widely available in urban centers and is recommended as part of routine antenatal care. The cost ranges from ₹1,500 to ₹3,000 and may be covered under maternity insurance plans. Follow-up diagnostic testing (chorionic villus sampling or amniocentesis) is available at major fetal medicine centers.
US: The American College of Obstetricians and Gynecologists (ACOG) recommends offering first-trimester screening to all pregnant women regardless of age. NT screening is often covered by insurance under the Affordable Care Act. NIPT (cell-free DNA screening) is a common next step for elevated-risk results.
UK: The NHS offers the combined screening test (NT measurement plus blood tests for PAPP-A and free beta-hCG) to all pregnant women between 11 and 14 weeks as part of the national screening programme. Follow-up diagnostic testing is provided through NHS fetal medicine units.
Disclaimer: This calculator provides estimates based on published reference charts and is intended for educational purposes. Always consult your obstetrician or midwife for interpretation of your specific ultrasound findings and clinical recommendations.
Frequently Asked Questions
What is nuchal translucency and why is it measured?
Nuchal translucency (NT) is the sonographic measurement of the fluid-filled space at the back of a fetal neck, measured during the first-trimester ultrasound scan between 11 and 14 weeks of pregnancy. It is a key screening marker for chromosomal abnormalities including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and Turner syndrome, as well as major structural abnormalities and fetal death risk.
How is the expected nuchal translucency calculated?
The expected nuchal translucency is calculated using the formula: Expected NT (mm) = 0.437 + (0.01969 × CRL), where CRL is the crown-rump length in millimeters. The calculator then compares the measured NT against the expected value and determines the percentile using validated reference charts from large population studies.
What is considered a normal nuchal translucency measurement?
A nuchal translucency measurement below the 95th percentile for the given crown-rump length is considered normal. For example, at 12 weeks gestational age (CRL approximately 55-60 mm), a normal NT measurement is typically 1.9 mm or less. Measurements at or above the 95th percentile indicate elevated risk and warrant further diagnostic testing.
What does it mean if my baby's NT is above the 95th percentile?
An NT measurement above the 95th percentile indicates elevated risk but is not a definitive diagnosis. Studies show that approximately 93% of pregnancies with NT between the 95th and 99th percentile result in healthy babies. Your doctor will recommend further tests such as NIPT (NIFTY), chorionic villus sampling (CVS), or amniocentesis to confirm or rule out chromosomal abnormalities.
Can a normal NT scan guarantee a healthy baby?
No, a normal nuchal translucency scan cannot guarantee 100% fetal health. NT screening is a risk assessment tool, not a diagnostic test. A comprehensive first-trimester screening combines NT measurement with maternal age, blood tests (PAPP-A and free beta-hCG), and presence of the nasal bone for a more accurate risk assessment.
What CRL range is valid for NT measurement?
Nuchal translucency measurement is clinically valid when the fetal crown-rump length (CRL) is between 45 mm and 84 mm, which corresponds to approximately 11 weeks to 13 weeks 6 days of gestational age. This calculator uses established reference charts based on CRL values within this range.
What is the difference between NT and nuchal fold?
Nuchal translucency (NT) is measured in the first trimester (11-14 weeks) and refers to fluid at the back of the fetal neck. The nuchal fold (NF) is measured in the second trimester (16-20 weeks) and refers to skin thickness at the back of the neck. Both are screening markers, but they are assessed at different gestational ages with different normal ranges.
Is the NT test covered by insurance in India, US, and UK?
In India, NT scan is part of the first-trimester screening and typically costs ₹1,500-₹3,000, with some insurance plans covering it under maternity benefits. In the US, NT screening is often covered by insurance under preventive maternity care per the Affordable Care Act, though co-pays may apply. In the UK, NT measurement is offered as part of the NHS combined screening test to all pregnant women free of charge between 11 and 14 weeks.