High-risk non-invasive Down syndrome screening failed

Down syndrome screening and minimally invasive DNA testing are both prenatal screening technologies. These two technologies complement each other and can further determine whether the baby in the pregnant woman's belly is healthy. If there is a high risk of Down syndrome, whether minimally invasive DNA testing can be successful is a concern for many pregnant women.

What is the situation when there is no basis for minimally invasive Down syndrome screening at high risk?

First of all, we need to understand that neither Down syndrome screening nor minimally invasive DNA testing can guarantee 20% accuracy. Only when the two complement each other can we further clarify whether the fetus's physical condition is normal.

In fact, for Down syndrome screening, it can help expectant mothers check whether the fetus has the risk of trisomy 21, trisomy 18 and open neural tube defect.

Although the cost of Down syndrome screening is not high compared to minimally invasive DNA testing, its accuracy and misdiagnosis rate are very high. Therefore, if a high risk of Down syndrome screening is found, it is very necessary to conduct a minimally invasive DNA test for re-examination.

In fact, the probability of minimally invasive diagnosis of high-risk Down syndrome screening is 98.9%. Therefore, even if the Down syndrome screening shows a high risk, there is a great probability that it can be detected through minimally invasive DNA testing, and only in very rare cases it cannot be detected through minimally invasive DNA testing. According to relevant survey findings, among 12,985 individuals at high risk of Down syndrome, only 108 cases of trisomy 21, 27 cases of trisomy 18 and 10 cases of trisomy 13 were found after NIFTY testing by BGI. Therefore, the probability of incorrect screening for Down syndrome is very high.

There were only 145 cases that were at high risk for minimally invasive DNA prenatal genetic testing. For pregnant mothers who were at high risk for Down syndrome, after minimally invasive prenatal testing, it was found that the probability of the fetus having chromosomal abnormalities was only 11.1 per thousand, which is close to 1% of the probability.

If the Down syndrome screening test shows a high risk, the doctor will only use it as a reference under certain circumstances. However, if it is time for minimally invasive DNA testing to show that pregnant women are at high risk, more detailed prenatal testing is needed. Common methods include umbilical vein blood puncture, chorionic villus sampling and amniocentesis. And for pregnant mothers, these are all necessary prenatal examinations, because these examinations are not only responsible for the fetus, but also for the personal safety of pregnant women.

Is there any relationship between the success rate of high-risk minimally invasive Down syndrome screening and the results of Down syndrome screening?

Down syndrome screening belongs to the second screening. The best time to do Down syndrome screening is between 16 and 18 weeks of pregnancy. What is done now is the second stage of Down syndrome, and the accuracy is about 70%. The main purpose of Down syndrome screening is to screen whether the fetus has congenital Down syndrome. Generally speaking, if the Down syndrome screening fails and the test results of the Down syndrome screening are high-risk, then a re-examination is required to verify whether the results of the Down syndrome screening are appropriate through amniocentesis or non-invasive DNA.

The accuracy of the results of Down syndrome screening is only 70%. In other words, the authenticity of Down syndrome screening is not high. However, even if the accuracy of Down syndrome screening is not high, it has nothing to do with the success rate of non-invasive DNA testing. However, Down syndrome screening indicates that the fetus is very likely to have Down syndrome, and non-invasive DNA is also used to check whether the fetus has Down syndrome. The success rate of non-invasive DNA is only half and half, that is, 50%.

Regardless of whether the Down syndrome screening has been passed or not, the results will not easily affect the selection of non-invasive DNA. However, if the fetus passes the Down syndrome screening, there is no need to do non-invasive DNA testing. In other words, the results of Down syndrome screening do not affect the results of non-invasive DNA testing. Some pregnant women may say, if that’s the case, why not do a non-invasive DNA test from the beginning to save the inconvenience. In fact, there are relatively few fetuses born with Down syndrome. What's more, the price of non-invasive DNA testing is relatively expensive. If the fetus has nothing wrong, it would be a waste to do non-invasive DNA testing.

Therefore, the success rate of high-risk minimally invasive Down syndrome screening is only 50%. Whether the Down syndrome screening is high risk or low risk, it will not easily affect the results of non-invasive DNA. Under normal circumstances, no one would do Down syndrome screening and would directly do non-invasive DNA testing because the price of non-invasive DNA testing is relatively high. Under normal circumstances, Down syndrome screening is done first, and only when the Down syndrome screening result is high-risk will non-invasive DNA be chosen to confirm the results of Down syndrome screening. There are two possible results for this certification, so the success rate of non-invasive DNA is 50%.