Noninvasive DNA test passed, but she gave birth to Down's son. What's going on here?

Is to extract pregnant women's serum, through the detection of related markers, comprehensive age and other factors to calculate the results, but the accuracy is too low, too many false positives, that is, to detect normal children as Down's syndrome.

(2) Amniocentesis

Literally, it can be understood that under the guidance of B-ultrasound, the needle is inserted into the uterus and the amniotic fluid is extracted for testing. This is also the standard of Down's screening fund, but it is risky for babies, and the abortion rate is about 0.3%.

Non-invasive DNA came out, and relevant policies and regulations were issued in April 20 14, and the detection was relatively mature and accurate, reaching more than 99%. Moreover, non-invasive DNA has obvious advantages over general Down's screening and amniocentesis, and has become a must-do item for pregnant mothers. However, if non-invasive DNA detects high risk, amniocentesis will be done for final confirmation before deciding whether to keep the baby.

(3) non-invasive DNA

However, the principle of non-invasive DNA has a defect. It needs 65,438+00 ml of pregnant women's blood, and then extracts the free DNA of the baby through the umbilical cord. The content is particularly low. If fraternal twins have received blood transfusion and bone marrow transplantation, the final result will be affected. Even if the probability is only one in ten thousand, millions of people will be tested every year, and a large number of Down's babies will be born. A heavy blow to this unfortunate family.

Fetal non-invasive DNA testing mainly includes the following manufacturers: Huada Gene, Berry, Yao Kang and Boao. The most reliable is Boao, which is the most expensive. The chromosomes of fetal non-invasive DNA detection mainly include 2 1, 18 and 13, which have the highest accuracy in prenatal screening. This is a good thing, greatly reducing the burden of amniocentesis. In particular, the detection rate of Down syndrome is as high as 99%, which is 2 1- trisomy. This point must be recognized by everyone. With the development of society, it will surely become the next necessary item for Down's screening. Don't deny its other contributions just because there are a few cases in which Down's children missed the test. After all, it is normal that the number of children with Down syndrome increases with the increase of samples, and the accuracy of Down syndrome screening is quite high.