What should I do if the Down syndrome screening indicates a high risk for trisomy 21?
Jun 13, 2019
Source: Cainiu Health
Dr. Zhang Chunxia
Introduction
What to do if the Down syndrome screening indicates a high risk for trisomy 21:
Down syndrome screening yields a risk probability—not a definitive diagnosis—calculated based on maternal serum markers, laboratory test results, gestational age, maternal weight, and other factors. A “high-risk” result does not equate to a confirmed diagnosis. A risk value greater than 1/270 is classified as high-risk, indicating an elevated likelihood that the fetus has Down syndrome.
The results of Down syndrome screening reflect a probability assessment—calculated based on maternal serum markers, laboratory test values, gestational age, maternal weight, and other factors—to estimate the risk of the fetus having Down syndrome. However, a “high-risk” result does not equate to a definitive diagnosis.
A screening result greater than 1/270 classifies the pregnancy as high-risk, indicating an elevated likelihood that the fetus has Down syndrome.
When Down syndrome screening yields a high-risk result, further diagnostic options include non-invasive prenatal testing (NIPT) and amniocentesis. NIPT involves drawing a peripheral blood sample from the mother, isolating cell-free fetal DNA, and analyzing chromosomes 21, 18, and 13 for numerical abnormalities.
Amniocentesis is a prenatal diagnostic procedure in which amniotic fluid is extracted to culture fetal cells and analyze chromosomal karyotypes; it provides a more accurate, definitive diagnosis. In contrast, NIPT is a highly sensitive screening test—not a confirmatory diagnostic test.
