Q. I am 35 years old and NT scan shows risk of Down's syndrome. What is the accuracy of NT scan?

Answered by
Dr. Kamalpreet Kaur Nagpal
and medically reviewed by Dr. Vinodhini. J
This is a premium question & answer published on Jun 15, 2020

Hi doctor,

I am 35 years old. Right now I am14 weeks pregnant. My doctor found out that my baby has a risk of down syndrome. In NT scan at 11 weeks 5 days the CRL was 48 mm and NT was 1.32 mm the double marker test report is showing

background risk T 21 1:369 and adjusted risk 1: 911.

T 18 background risk is 1:4357 and adjusted risk is 1:238.

T13 background risk is 1:10257 and adjusted risk is 1:3524.

Doctor did NIPT after this report. Can you tell me how accurate the results are and why NIPT was done?



Welcome to

Your report in the link is not readable (attachment removed to protect patient identity). However, the values that you have written in the query seem to be all within range.

For T21 cut off is 1 in 250 and NT 1.3 mm is also fine. May be you are 35 and doctor wants to be doubly sure for your safety.

Thank you doctor,

But she said trisomy 18 is on the higher side. Why its background risk is 1:4357 and the adjusted risk is 1:238.



Welcome back to

Your report is showing the values for low risk (attachment removed to protect patient identity). Cut off for trisomy 18 and 13 is 1:100 and for T21 1:250. NT is within normal. Nasal bone is seen. Ductus venosus waveform not mentioned. These are the things we see in the level 1 scan. Other risk factors have also been mentioned which can occur according to the gestation period. The only thing which is worrying in the present report is that amniotic fluid is lesser in the given report.

I feel you should start conservative management with your doctor and then wait for level 2. anomaly scan which is done at 18 to 22 weeks. You better get it done between 18 and 19 weeks and then things will be more clear.

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