Q. What does high risk 1:50 trisomy 21 mean?

Answered by
Dr. Sravanthi Nuthalapati
and medically reviewed by Dr. Vinodhini. J
This is a premium question & answer published on Apr 23, 2020

Hello doctor,

What does high risk 1:50 trisomy 21 mean, at an age of 32 and 18 weeks pregnancy?



Welcome to

I totally understand your anxiety. But please do not panic.

The risk for Trisomy 21 (or in other words Down's syndrome) mentioned is 1:50, which is above the general population risk of 1:250. In other words, if we take a general population, and consider any women in general, there is a risk that one in 250 women may have a baby who is affected with Down's syndrome. But in your case, the risk appears to be increased compared to the general population which needs to be evaluated further.

This is a test that determines the risk, which means it is only a screening test and not a confirmatory test. Meaning, the baby may or may not be affected by Down's but the risk appears to be high compared to the normal population.

It would have been helpful if you had the shared few more details like your period of gestation of your pregnancy, when and at what gestation was the test taken, and any previous scan reports in the first trimester you have done. Kindly share the reports to guide you better. And, also provide details if you had any previous pregnancy, or miscarriages, etc.

Now coming to confirming this, for definitive and accurate methods, it includes amniocentesis with karyotyping and FISH test, which are little expensive tests and not done in all individuals except those with high risk for Down's syndrome. For this test to be done, the water around the baby inside the uterus is taken in a small amount which contains the shed cells of the baby and are cultured so as to do the chromosomal analysis of the cells. This is an invasive test as it comes with the risk of 0.2-1% risk of miscarriage as we are putting a needle inside the uterus.

Another recently introduced test which almost as closely accurate to this is NIPT (noninvasive prenatal test), which is again a screening test but highly accurate and involves only testing your blood for fetal cell-free DNA and then they are analyzed for the same.

You can consult a fetal medicine expert or your gynecologist for further information on these and necessary timely action.

I hope this helps.

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