What tests should be done after Down syndrome screening?

Down syndrome screening is currently a common examination item. It can be used to determine the patient’s current physical condition and choose appropriate methods for treatment. Generally, what kind of examination is done after Down syndrome screening depends on personal physical changes and the results of the examination. Therefore, it is very important to check the results. Most people cannot understand the results, so what are the results and accuracy?

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Currently, the Down syndrome screening test tests the concentration of alpha-fetoprotein (AFP) and human chorionic gonadotropin (β-hCG) in the pregnant woman's blood, and combines it with the pregnant woman's age to use a computer to accurately calculate the risk of each pregnant woman carrying a fetus with Down syndrome. The normal value of alpha-fetoprotein should be 0.4~2.5MoM. The lower the test value, the higher the chance that the fetus will suffer from Down syndrome. The higher the level of chorionic gonadotropin, the higher the chance that the fetus will have Down syndrome.

In addition, the doctor will input the alpha-fetoprotein value, human chorionic gonadotropin value, as well as the pregnant woman's age, weight, and weeks of pregnancy into the computer, which will calculate the risk of the fetus developing Down syndrome. If the test results show that the risk is lower than 1/270, it means that the risk is relatively low and the chance of the fetus developing Down syndrome is less than 1%. However, if the risk is higher than 1/270, it means that the fetus is at high risk of disease and further amniocentesis or chorionic villus sampling should be performed.

Accuracy

Down syndrome screening can detect 60-70% of children with Down syndrome. It should be made clear that the Down syndrome screening test can only help determine the chance that the fetus has Down syndrome, but it cannot determine whether the fetus has Down syndrome. That is to say, when the blood test index is high, the chance of having a Down syndrome baby is higher, but it does not mean that there must be something wrong with the fetus. Just as older pregnant women over 35 years old have a higher chance of having Down syndrome babies, it does not mean that their fetuses will definitely have problems. On the other hand, even if the test index is normal, it cannot guarantee that the fetus will not be sick.

Pregnant women whose Down syndrome screening index exceeds the normal level should undergo amniocentesis or chorionic villus sampling. Only if the results of amniocentesis or chorionic villus sampling are normal can the possibility of Down syndrome be 100% ruled out.

With the continuous development of technology, in addition to Down syndrome screening, non-invasive prenatal genetic testing can now be used to detect Down syndrome and chromosome 18 and 13 abnormalities. Non-invasive prenatal genetic testing can detect more than 99% of babies with Down syndrome. Like Down syndrome screening, the test only requires a blood draw from the arm, avoiding the increased risk of miscarriage caused by amniocentesis or chorionic villus sampling.

For older pregnant women and those at high risk of Down syndrome, non-invasive prenatal genetic testing is another new option to amniocentesis. For ordinary pregnant women, non-invasive prenatal genetic testing can also be used as a better method for Down syndrome screening.