DNA based prenatal screening technology, the first step to know your baby

Non-invasive prenatal genetic testing (NIPT) is the use of next-generation DNA sequencing technology to sequence fetal free DNA (cffDNA) extracted from maternal peripheral plasma, and perform biological information analysis on the sequencing results, which can obtain fetal genetic information. Such as Down syndrome, Rh blood type, abnormal sex chromosomes, and fetal sex.

Humans have a long-standing demand for genetic disease testing: in the 1970s, the birth of amniocentesis allowed doctors to detect chromosomal abnormalities in the second trimester and identify genetic disease risks. In the 1980s, a new detection technique called Chorionic Villus Sampling could identify chromosomal abnormalities early in pregnancy. Both amniocentesis and chorionic sampling can provide complete genetic information of the fetus, and the test results are accurate. However, because they are all invasive tests, pregnant women undergoing tests have to bear a certain risk of miscarriage, requiring medical staff to be quite professional. Because NIPT only requires simple blood drawing operations, genetic testing based on this technology is more popular in developing countries where medical personnel are scarce.

    Early detection of chromosomes and other genetic abnormalities creates conditions for better pregnancy care, and at the same time, it becomes possible to mobilize limited medical resources more reasonably to serve the health management of newborns with genetic abnormalities. In some countries, early detection has created the possibility of an earlier and safer termination of pregnancy, including the use of drugs.

Humans have been demanding genetic disease testing for a long time: but a new type of non-invasive "non-invasive prenatal genetic testing" may change this status quo. Its principle is that from the beginning of pregnancy, some fetal cells will enter the maternal blood through the placenta. But the number of these cells is very small, not enough for testing. The breakthrough of this technology is that it can identify "non-cellular" fetal DNA-that is, fetal DNA outside of cells. When this non-cellular DNA is separated from the mother’s plasma, 10% to 20% of it is DNA from the fetus. In other words, if the mother’s DNA can be separated from the fetus’s DNA, we can sequence the fetus’s DNA completely.

But the current technology has not yet achieved this accuracy. So this technology can only detect DNA that is abnormal or unlikely to belong to the mother. It can be used to detect the sex of the fetus-because the mother has two X chromosomes, if a DNA fragment from the Y chromosome is found in the test, the baby will be a boy, otherwise, it is most likely a girl.

This technology can also be used to detect genetic diseases caused by chromosomal abnormalities. DNA-based prenatal blood testing can be used to screen high-risk women for Down’s syndrome and similar chromosomal abnormalities. This testing method has now been slowly introduced to the general pregnant population; recently, researchers from the United Kingdom Through research, it is found that this non-invasive detection method may be effective and appropriate for all pregnant women, and it will not be affected by the mother's age or risk factors. The relevant research was published in the international journal Genetics in Medicine.

However, since this test is based on statistical results, false negative results are unavoidable. In other words, sometimes the fetus may have chromosomal abnormalities, but it will not be detected. But overall, the probability of false negatives is relatively low. In normal childbearing age pregnancy, the probability of false negatives is about 1 in 90000. Therefore, the results of this detection technology are still reliable.

There are currently three types of non-invasive prenatal genetic testing available in the United States:

1) Harmony pregnancy test: This is a blood test to screen for Down syndrome, trisomy 18 and trisomy 13. Its technology is to analyze whether the fetal DNA is abnormal by identifying specific cell-free DNA fragments.

2) MaterniT 21 PLUS test: In addition to screening for common trisomy syndrome, this test can also detect the sex of the fetus and screen for genetic diseases caused by abnormal sex chromosomes. The technology used is also to identify genetic defects by sequencing cell-free DNA.

3) Panorama pregnancy test: In addition to detecting gender and screening the above-mentioned trisomy syndrome and sex chromosome syndrome, it can also detect chromosome microdeletions and triploids (with three sets of chromosomes). Its technology also determines the copy number of chromosomes by analyzing single nucleotide polymorphisms, thereby identifying genetic defects in the fetus.

The above content is reproduced from: China Inspection Global Network