The nuchal translucency (NT) scan is an ultrasound exam done during the first trimester of pregnancy that measures the amount of fluid behind the fetal neck. It can help screen for fetal anomalies and genetic conditions, such as omphalocele or Down syndrome, for example.
An abnormal value is typically considered to be 3 mm or greater (or >99th percentile for gestational age), however different hospitals and clinics may use slightly different cutoff values. If the NT result is abnormal, procedures like chorionic villus sampling (CVS) and amniocentesis may be indicated to help confirm a diagnosis.
Make sure to talk to your obstetric provider about your NT results and whether any additional testing is necessary.
![ultrasonographer performing a pregnancy ultrasound](https://image.tuasaude.com/media/article/os/rz/translucencia-nucal_22571.jpg?width=686&height=487)
Indications for testing
The nuchal translucency scan can help determine the risk for:
- Down syndrome;
- Cardiac anomalies;
- Patau syndrome;
- Diaphragmatic hernia;
- Edwards syndrome;
- Noonan syndrome.
The NT scan is a screening tool used to help identify those at risk for having a baby with certain genetic disorders or birth defects. It cannot be used to diagnose any specific condition.
An abnormal NT result may prompt your OBGYN to recommend diagnostic procedures like chorionic villus sampling (CVS) or amniocentesis to confirm or rule out the presence of a genetic disorder.
When the test is performed
The nuchal translucency scan should be done between 11 weeks and 13 weeks 6 days of pregnancy, when the fetus measures between 45 and 84 mm.
How the test is done
The nuchal translucency measurement is done as part of the routine first trimester ultrasound, in which the doctor measures the fetus and checks for normal signs of fetal development.
During the ultrasound, the doctor will also measure the pocket of fluid at the back of the fetus's neck, known as the nuchal translucency.
Reference values
A nuchal translucency less than 3 mm is generally considered to be normal.
NT measurements above 3 mm are generally considered to be abnormal and can indicate an increased risk for genetic disorders or congenital anomalies.
Different hospitals and clinics may use different cutoffs for what is considered a normal NT measurement. Reference values may also vary based on gestational age and pregnancy history.
What does an abnormal result mean?
An abnormal nuchal translucency is typically any result greater than 3 mm, although reference values may vary.
This result only indicates an increased risk for genetic conditions or birth defects. It does not necessarily mean that your baby has any of these conditions. It is important to discuss any abnormal result with your OBGYN or midwife. You may be referred to a maternal fetal medicine specialist (MFM) or genetics counselor to further discuss your results.
Other factors will be taken into consideration to further determine your risk, such as maternal age and presence of a nasal bone on first trimester ultrasound. The first trimester ultrasound is also used to examine ductus venosus blood flow and identify tricuspid regurgitation, which can also help predict the risk for genetic disorders and congenital anomalies.