Is it still possible to screen for Down syndrome if the NT scan is missed?

Feb 26, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

Nuchal translucency thickness examination is usually performed between the 11th and 14th weeks of pregnancy. It primarily uses ultrasound to measure the amount of subcutaneous fluid accumulation in the fetal neck to assess the risk of chromosomal abnormalities. If this time window is missed, but the gestational age has not exceeded 20 weeks, other screening methods such as second-trimester serum screening or non-invasive prenatal genetic testing may be used.

NT scan generally refers to the nuchal translucency thickness examination. Missing this examination usually still allows for screening for Down syndrome through other methods.

The nuchal translucency thickness examination is typically performed between weeks 11 and 14 of pregnancy. It primarily uses ultrasound to measure the amount of fluid accumulation under the fetal neck skin to assess the risk of chromosomal abnormalities. If this time window is missed but the gestational age has not exceeded 20 weeks, other screening methods such as mid-trimester serum screening or non-invasive prenatal genetic testing can be used to assess the risk of Down syndrome.

In addition to Down syndrome screening, pregnant women can also choose non-invasive DNA screening before 22 weeks of pregnancy. Non-invasive DNA screening is generally more accurate and can detect chromosomal abnormalities such as trisomy 21, trisomy 18, and trisomy 13. It should be noted that if the pregnant woman is over 35 years old or has other high-risk factors, additional prenatal diagnostic procedures such as amniocentesis or chorionic villus sampling may be required.

Prior to undergoing any prenatal screening or diagnosis, pregnant women should consult with a qualified physician to ensure accurate and reliable information regarding their pregnancy. Pregnant women should maintain a positive mindset and follow the guidance of a qualified physician for subsequent examinations and diagnostic procedures.

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What are the components of prenatal screening for Down syndrome?

Under normal circumstances, prenatal screening programs for Down syndrome include serological screening for Down syndrome, ultrasound NT examination, non-invasive prenatal genetic testing, amniocentesis, and cordocentesis. It is advisable to undergo comprehensive preconception checkups before pregnancy, including chromosomal testing for both partners, to understand one's own physical condition. If there is a family history of genetic disorders or other high-risk factors, timely consultation with a physician and appropriate interventions should be considered.

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What does "borderline risk in Down syndrome screening" mean?

In general, a borderline risk in Down syndrome screening refers to a specific range of results obtained during prenatal screening for Down syndrome, where the result falls between the normal range and the high-risk range. A borderline risk indicates that the fetus has a relatively higher risk of chromosomal abnormalities such as Down syndrome, but it does not confirm a diagnosis. Pregnant women should undergo further prenatal diagnostic testing to clarify the situation.