π€° Nuchal Translucency Interpreter
What your NT measurement means in context.
For informational purposes only, not medical advice. Consult a healthcare professional.
Nuchal translucency is the fluid-filled space at the back of the fetus's neck, measured by ultrasound at 11 to 13+6 weeks. Thicker NT correlates with hihigher chances of chromosomal conditions (Down syndrome in particular), heart defects, and some genetic syndromes. Under 3.0 mm is typically reassuring; 3.5 mm and above triggers offers of diagnostic testing and detailed anatomy scans.
Enter the NT in millimeters and the gestational age in weeks. The interpreter places the measurement in its band and explains where it fits in combined first-trimester screening (NT plus blood markers PAPP-A and free beta-hCG plus maternal age). NT is a screening input, never a diagnosis.
How to Use This Calculator
Find the NT measurement in millimeters on the first-trimester ultrasound report and confirm the gestational age (valid window 11 to 13+6 weeks, CRL 45-84 mm). Enter both. Read the band and the recommended next step. Discuss any increased result with your OB or a maternal-fetal medicine specialist, not with worry alone.
Enter the NT measurement in mm from the ultrasound report.
Enter gestational age in weeks.
Read the interpretation band.
Follow the next step: routine screening or specialist discussion.
Why Neck Fluid Predicts Risk
NT >= 3.5 mm: diagnostic testing offered
First-trimester fetuses with trisomy 21, 18, or 13, Turner syndrome, and several cardiac and genetic conditions tend to accumulate more nuchal fluid, for reasons involving lymphatic development and cardiac function. Nicolaides' Fetal Medicine Foundation standardized the measurement technique (mid-sagittal plane, neutral fetal position, CRL 45-84 mm) because millimeters of difference change risk estimates. Combined with maternal age and serum markers, first-trimester screening detects roughly 85-90% of Down syndrome cases at a 5% screen-positive rate. Cell-free DNA (NIPT) is more accurate for the common trisomies but does not assess anatomy the way NT plus ultrasound does.
Worked Example
NT 2.1 mm at 12 weeks: 2.1 mm reads "Typically reassuring (<3.0 mm)" within the Valid window (11-13+6 weeks) - CRL 45-84 mm required. The key context is NT is one part of combined first-trimester screening: NT alone never diagnoses anything, and most babies with mildly increased NT are healthy. At 4.0 mm the guidance flips to Routine combined screening follow-up.
Reading Your NT Band
Under 3.0 mm at the right gestation is reassuring and the commonest result. Three to 3.4 is borderline: follow-up discussion, and many centers watch with detailed anatomy ultrasound. At or above 3.5, guidelines offer diagnostic testing (CVS or amniocentesis) plus fetal echocardiography, because cardiac anomalies rise with NT even when chromosomes are normal. Markedly increased NT (6+) carries higher risks across categories. Most increased-NT pregnancies still end with healthy babies: screening shifts probabilities, it does not deliver verdicts.
Screening Needs Counseling, Not Googling
An increased NT result deserves a prompt appointment with your OB or maternal-fetal medicine for proper risk counseling and testing options. Do not make decisions from a single measurement interpreted alone. Genetic counselors specialize in exactly these conversations. For informational purposes only, not medical advice. Consult a healthcare professional.
Related tools: pregnancy due date calculator, IVF due date calculator and mean sac diameter dating.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is a normal nuchal translucency?
Under 3.0 mm at 11 to 13+6 weeks is typically reassuring. The measurement must be taken in the valid CRL window.
What does increased NT mean?
Higher chances of chromosomal conditions, heart defects, or genetic syndromes. Most increased-NT pregnancies still have healthy outcomes.
When is the NT scan done?
Between 11 weeks and 13 weeks 6 days gestation, when the fetus measures 45-84 mm crown-rump length.
Is NT screening diagnostic?
No. It is a screening test estimating risk. CVS or amniocentesis give diagnostic answers about chromosomes.
What is the difference between NT and NIPT?
NT is an ultrasound marker plus blood work screening broadly; NIPT analyzes fetal DNA in maternal blood and is more accurate for trisomies 21, 18, 13.
Can NT be too early or late?
Yes: outside 11-13+6 weeks (CRL 45-84 mm) the measurement is not valid for risk calculation.
What happens if NT is 3.5 mm or more?
Guidelines offer diagnostic testing and detailed anatomy including fetal echocardiography, with genetic counseling.
Does high NT always mean a problem?
No. Many babies with increased NT are born healthy; the finding raises probability and prompts further evaluation.
What happens if the NT measurement is high?
A high NT (above about 3.5 mm) raises the calculated risk but does not diagnose anything; most babies with thick NT are born healthy. The usual next steps are cell-free DNA screening or diagnostic testing (CVS or amniocentesis), plus a detailed anatomy scan and fetal echocardiogram around 20 weeks, since thick NT also links to heart defects.
Can the NT scan be done too early or too late?
Yes, the window is strict: 11 weeks to 13 weeks 6 days, with the fetus measuring 45 to 84 mm crown-rump length. Earlier, the fluid space is too small to measure reliably; later, it normally resolves and the measurement loses meaning. If you miss the window, cell-free DNA and the anatomy scan become the screening path instead.