What fetal conditions does the Down syndrome screening test detect?
The Down syndrome screening test is a widely recognized prenatal examination in modern society—especially among women of childbearing age, most of whom are familiar with what it entails. However, many women who have not yet given birth remain relatively unfamiliar with Down syndrome screening. So, precisely what fetal conditions does the Down syndrome screening assess?
What fetal conditions does the Down syndrome screening assess?
Commonly referred to as “Tang screening,” Down syndrome screening is a critical component of routine prenatal care, primarily designed to identify pregnancies at increased risk for certain congenital genetic disorders. It is divided into two categories: early-stage and mid-stage Down syndrome screening.
Early Down syndrome screening is performed at approximately 12 weeks’ gestation, requiring fasting blood collection and ultrasound measurement of nuchal translucency (NT). Mid-stage screening takes place between 15 and 20 weeks’ gestation, also involving fasting blood collection. Across all Down syndrome screening protocols, the primary objective is to estimate the fetal risk for trisomy 18, trisomy 21 (Down syndrome), and open neural tube defects. The calculated risk values are then compared against established population-based cutoffs to generate a risk assessment. A low-risk result generally indicates that the fetus is unlikely to be affected. A high-risk result warrants further diagnostic testing—typically amniocentesis—for confirmation. For borderline or intermediate-risk results, non-invasive prenatal testing (NIPT) using cell-free fetal DNA is usually recommended for more accurate risk stratification.
It is essential to perform the Down syndrome screening within the optimal gestational window—ideally between 16 and 20 weeks. Missing this timeframe may compromise test accuracy. Fetal size—either too large or too small for gestational age—can also affect screening reliability. We hope this information proves helpful!
