Is the Trisomy 21 test with a ratio of 1/159 dangerous and what to do?

Ask
Hello doctor! I am 38 years old and pregnant for the 3rd time. I have a Trisomy 21 test, the ratio is 1/159. So the doctor asked me, is the Trisomy 21 test, the ratio of 1/159, is it dangerous and what should I do next? Looking forward to your advice, thank you doctor!
Le Thi Hong Thai (1982)
Answer
Hello, doctor would like to answer the question: “Is the Trisomy 21 test with a ratio of 1/159 dangerous and what to do? ” as follows:
Mothers in the first trimester of pregnancy, at 11-13 weeks of pregnancy, are often advised by obstetricians and gynecologists to do a double test prenatal screening test to help assess the risk of genetic diseases. include: Down syndrome (Trisomy 21); Edward's syndrome (Trisomy 18); Patau syndrome (Trisomy 13). These are the most common chromosomal abnormalities in children.
The accuracy of Double Test results combined with ultrasound and other pathological information is capable of detecting about 85 - 90% of Down syndrome cases, the false positive rate is 5%.
With Edwards and Patau syndrome, the detection rate is 95%, the false positive rate is 0.3%. The fetal risk threshold for Down syndrome is 1/250, your test has a Trisomy 21 ratio of 1/159 which is high risk, however this is only a screening method, not must be a diagnostic method, therefore you need to do additional high-precision screening methods or other accurate diagnoses to reach appropriate conclusions, counseling and interventions. More accurate screening methods to check the risk of birth defects due to chromosomal abnormalities after the commonly used Double Test include: Noninvasive screening test NIPT; Amniocentesis, chorionic villus biopsy.
If you still have questions about prenatal screening tests, you can go to a hospital under Vinmec Health System to get checked. Thank you for trusting and sending questions to Vinmec. Wishing you lots of health. Best regards!

Answered by Master, Doctor Do Thi Hoang Ha - Doctor of Biochemistry - Laboratory Department, Vinmec Hai Phong International General Hospital