Can non-invasive DNA testing diagnose trisomy 21?

Mar 04, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

Non-invasive DNA testing accurately assesses the risk of fetal chromosomal abnormalities, including trisomy 21, by analyzing fetal cell-free DNA in the mother's blood. This testing method offers high sensitivity and specificity, effectively identifying high-risk fetuses. Therefore, it is widely used in clinical settings as a primary screening tool.

Trisomy 21 generally refers to Trisomy 21 syndrome. Non-invasive DNA testing usually cannot definitively diagnose Trisomy 21 syndrome but can serve as an auxiliary method to help assess the condition. If experiencing any physical discomfort, it is recommended to seek medical attention at a hospital promptly and follow the doctor's instructions for treatment.

Non-invasive DNA testing analyzes fetal free DNA in the pregnant woman's blood to accurately assess the risk of fetal chromosomal abnormalities, including Trisomy 21 syndrome. This testing method has high sensitivity and specificity, effectively identifying fetuses at high risk, thus it is widely used in clinical settings as a primary screening tool. Although non-invasive DNA testing has a very high accuracy rate, it remains a screening method rather than a diagnostic method.

When non-invasive DNA testing detects potential chromosomal number abnormalities, pregnant women are advised to undergo confirmatory tests such as amniocentesis for a definitive diagnosis. Amniocentesis can analyze the chromosomal core of fetal amniotic fluid cells, thereby providing a more accurate conclusion. The specimen collected for non-invasive DNA testing is the pregnant woman's blood, which contains maternal, fetal, and placental components that may interfere with the accuracy of the test results.

Pregnant women should fully understand the characteristics and limitations of non-invasive DNA testing before undergoing the test and make informed decisions under the guidance of a qualified physician.

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What causes trisomy 21 syndrome?

The occurrence of trisomy 21 syndrome is related to maternal age. In older pregnant women, chromosomal abnormalities in the oocytes can lead to trisomy 21 syndrome. These abnormal chromosomes can be directly inherited, resulting in offspring with trisomy 21 syndrome. Other contributing factors include miscarriage, exposure to strong radiation during pregnancy, inadvertent use of teratogenic drugs, severe viral infections, or chemical pollution.

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What is the incidence rate of trisomy 21 syndrome?

The incidence rate of trisomy 21 syndrome is approximately 0.5% to 0.6%. Trisomy 21 syndrome usually refers to a condition caused by chromosomal abnormalities during embryonic development. Under normal circumstances, human cells contain 23 pairs of chromosomes; however, in trisomy 21 syndrome, there is an extra chromosome in the 21st pair, a condition clinically known as Down syndrome.

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Normal range for trisomy 21 syndrome

Trisomy 21 syndrome, also known as congenital idiocy or Down syndrome, is a disease caused by abnormal autosomes. It mainly results from having three copies of chromosome 21 instead of the normal pair. Affected fetuses will have intellectual disabilities after birth. Screening for Down syndrome during pregnancy is necessary to assess the risk of trisomy 21. The normal risk range for trisomy 21 is less than 1:245.

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Normal range for trisomy 21 risk

There are two methods for assessing the risk of fetal trisomy 21 during pregnancy: Down syndrome screening and non-invasive DNA testing. These two tests use different methodologies, resulting in different risk estimates. In Down syndrome screening, the cutoff value for trisomy 21 risk is defined as 1:270; values below this threshold are considered low risk and normal, while values above it indicate high risk.

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What is the normal value for Down syndrome screening (Trisomy 21)?

The Down syndrome screening is typically performed between weeks 16 and 20 of pregnancy. For trisomy 21, a normal (low-risk) result is defined as a risk value less than 1/1,000. A result between 1/270 and 1/1,000 is considered borderline risk. If the measured risk exceeds 1/270, the screening indicates a high risk for Down syndrome, meaning the fetus has a significantly increased probability of having Down syndrome.

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What is Down syndrome?

Down syndrome is actually a genetic disorder known as trisomy 21, also called Down syndrome. Humans normally have 23 pairs of chromosomes, totaling 46, but individuals with Down syndrome have an extra copy of chromosome 21. Characteristics of Down syndrome include wide-set eyes, frequent tongue protrusion, intellectual disability, and strong survival ability.

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Trisomy 21 and Trisomy 18: Differences

Trisomy 21 and Trisomy 18 may differ in aspects such as chromosomal abnormalities, clinical manifestations, patterns of inheritance, diagnostic methods, and prognosis. Trisomy 21 involves an extra copy of chromosome 21, meaning individuals with this condition have three copies of chromosome 21 in their cells instead of the usual two. Trisomy 18, on the other hand, involves an extra copy of chromosome 18.

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What to do if the Down syndrome screening indicates a high risk for trisomy 21?

Under normal circumstances, a high-risk result for trisomy 21 in Down syndrome screening may be caused by factors such as advanced maternal age, miscalculation of gestational age, chromosomal abnormalities, exposure to teratogenic substances during pregnancy, or genetic factors. Pregnant women can visit a reputable hospital to choose further diagnostic tests or medical interventions. In daily life, it is important to avoid exposure to harmful substances during pregnancy, maintain a regular作息 (sleep-wake cycle), and follow a balanced diet.

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