What are the differences between Down syndrome screening and non-invasive DNA testing?
Jul 19, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
The Down syndrome screening calculates the risk of the fetus having Down syndrome and other diseases by testing indicators such as maternal serum alpha-fetoprotein and human chorionic gonadotropin levels in the pregnant woman's blood, combined with information including the mother's age and weight; non-invasive DNA testing isolates fetal free DNA from the pregnant woman's peripheral blood and uses genetic sequencing technology to analyze fetal chromosomal abnormalities.
Non-invasive DNA testing, also known as non-invasive prenatal testing (NIPT), differs from Down syndrome screening in several aspects including testing principles, accuracy, target population, scope of detection, and optimal testing time. A detailed comparison is as follows:
1. Testing Principles: Down syndrome screening assesses the risk of fetal chromosomal abnormalities such as Down syndrome by measuring maternal blood markers including alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG), combined with maternal age, weight, and other factors. Non-invasive DNA testing analyzes fetal cell-free DNA extracted from maternal peripheral blood using advanced gene sequencing technology to detect fetal chromosomal abnormalities.
2. Accuracy: Down syndrome screening has relatively lower accuracy with potential for both false positives and false negatives, often requiring further diagnostic testing for confirmation. NIPT demonstrates higher accuracy for common trisomies, with a significantly lower false positive rate, thereby providing a more precise assessment of fetal chromosomal abnormality risks.
3. Target Population: Down syndrome screening is generally recommended as an initial screening tool for the general pregnant population, particularly for low-risk individuals under the age of 35. NIPT is recommended for pregnant women with high-risk results from Down syndrome screening, those who missed the optimal screening window, or those with a family history of genetic disorders.
4. Scope of Detection: Down syndrome screening primarily evaluates the risk of trisomy 21, trisomy 18, and open neural tube defects. NIPT can detect common trisomies including trisomy 21, trisomy 18, and trisomy 13, with some advanced tests also capable of identifying other chromosomal numerical abnormalities and microdeletions or microduplications.
5. Optimal Testing Time: Down syndrome screening is typically performed between 15 to 20 weeks of gestation when blood biomarkers are most stable, ensuring effective screening. NIPT can be conducted earlier, between 12 to 22 weeks of pregnancy, offering a broader testing window.
If either Down syndrome screening or NIPT yields abnormal results, further diagnostic procedures such as amniocentesis should be promptly performed to confirm the diagnosis and implement appropriate measures to ensure maternal and fetal health.
