If you had a nuchal translucency (NT) ultrasound in the first trimester of pregnancy, it is important to understand what it means if the measurement is “increased” or “abnormal”.

What is an increased NT?

In Ontario, the current cut-off for the NT measurement to be considered “increased” is 3.5mm. If the measurement is increased, your health care provider will discuss options for further testing and follow-up.

Illustration adapted from Genetic Counseling Aids, 7th Edition, Copyright 2020, permission for use granted by Greenwood Genetic Center

What an increased NT might mean

Measuring the NT in the first trimester of pregnancy is one way to screen pregnancies for some common chromosome and structural differences, including:

• trisomy 21 (Down syndrome)
• other chromosome differences – e.g., trisomy 18, trisomy 13, Turner syndrome, triploidy
• other genetic conditions – e.g., Noonan syndrome
• structural abnormalities – e.g., cardiac (heart) defects

It is important to know that an increased NT measurement can also be seen in healthy pregnancies. If invasive diagnostic testing rules out chromosome differences, the vast majority of babies with an increased NT measurement will have a healthy outcome.

Next steps

If you have an increased NT measurement, you should be offered a referral to a genetics or Maternal Fetal Medicine (MFM) clinic to discuss options for further testing. Any further testing is optional but may include:

• invasive diagnostic testing – e.g., chorionic villus sampling (CVS) or amniocentesis
• non-invasive prenatal testing (NIPT) - NIPT is funded by OHIP when the NT measurement is increased, and can be ordered by your pregnancy care provider or geneticist / Maternal Fetal Medicine (MFM) specialist
• detailed anatomy ultrasound
• fetal echocardiogram - specialized ultrasound of the fetal heart

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