Is it acceptable to proceed directly with the Down syndrome screening without performing nuchal translucency (NT) measurement?

Nuchal translucency (NT) screening is one of the routine prenatal examinations and a critically important test for detecting fetal developmental abnormalities during pregnancy. The Down syndrome screening (also known as “Tang screening”) involves analyzing maternal blood to measure serum levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3). These biomarkers, combined with maternal factors—including age, weight, and gestational age—are used to assess the risk of chromosomal abnormalities such as Down syndrome (trisomy 21) and neural tube defects (NTDs). So, can pregnant women skip NT screening and proceed directly to Down syndrome screening? Below, we address this question.

Can Down syndrome screening be performed without prior NT screening?

Generally speaking, although both NT and Down syndrome screening aim to detect fetal structural or chromosomal abnormalities, they differ significantly in timing and methodology. Both tests are recommended during pregnancy, and skipping NT screening to proceed directly to Down syndrome screening is not advised. Performing NT screening first—followed by Down syndrome screening—provides more comprehensive insight into fetal development. To safeguard optimal fetal growth and maternal health, it is essential to follow medical recommendations, consider individual health status, register at a hospital early in pregnancy, and attend scheduled antenatal visits regularly. Furthermore, NT screening is typically conducted around week 12 of gestation and involves measuring the thickness of the nuchal translucency—the fluid-filled space at the back of the fetal neck—to evaluate the likelihood of congenital anomalies. If NT results are abnormal, Down syndrome screening is generally not recommended; instead, further diagnostic testing—such as non-invasive prenatal testing (NIPT) or amniocentesis—is warranted. Even with normal NT findings, additional anomaly screening—such as a detailed four-dimensional (4D) ultrasound—is still required.

Knowledge Extension: Key Considerations for NT Screening

1. Fasting is not required

NT screening is an ultrasound-based examination and does not involve blood sampling, dietary restrictions, or fluid intake limitations—none of which affect the accuracy of the results. Therefore, fasting before the exam is unnecessary. However, it is advisable to schedule the NT scan in advance. Excessively long waiting times may cause the examination to fall outside the optimal gestational window, thereby compromising result reliability.

2. Timing is critical

NT screening must be performed between weeks 11 and 14 of gestation. Before week 11, the fetus is too small for reliable visualization of the nuchal translucency. After week 14, progressive fetal development may lead to reabsorption of excess fluid in the nuchal region, potentially obscuring or diminishing the nuchal translucency measurement and thus compromising diagnostic accuracy. Therefore, expectant mothers should ideally undergo NT screening between weeks 11 and 14 to ensure optimal test sensitivity and reliability.

The above outlines whether Down syndrome screening can be performed without prior NT screening. We hope this information is helpful to you.