182| [Medicine] Obstetrics: Non-invasive DNA testing

The 182nd original after the revision...

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Noninvasive DNA testing is a type of prenatal screening designed to screen for birth defects and genetic disorders. Prenatal diagnostic techniques include chorionic sampling and amniocentesis, both of which are cell samples and have a small risk of miscarriage and complications.

Noninvasive DNA testing is a blood draw test, so there is no risk to the mother and fetus.

The principle of noninvasive DNA testing is that there is a small amount of fetal DNA in the mother's blood, which belongs to the screening experiment, can not give an accurate answer, can only indicate the risk of some abnormalities in the fetus, and does not guarantee that it will be sick or not.

Sometimes the test results show abnormalities, but everything is normal after the fetus is born, which is a false positive. Sometimes no abnormality is found, but the fetus is born by abnormality, which is false negative.

In addition, because this method examines both fetal and maternal cfDNA (cell free DNA), it is possible to detect chromosomal abnormalities of the mother.

Noninvasive DNA is done after the fetus's cfDNA reaches a sufficient proportion (at least 4%) in the mother's blood, usually until the 10th week of pregnancy, and the domestic regulations generally do it at 12-22 weeks of pregnancy.

It is mainly used to screen for the following 3 types of birth defects:

1. Down syndrome: one more copy of chromosome 21, the child will have learning disabilities and other health problems (heart and digestive tract abnormalities)

2. Edward syndrome: Chromosome 18 has one more copy, the child is born small and fragile, there are many serious health problems, only 10% of the children can live past the age of 1.

3. Batao syndrome: there is one more copy of chromosome 13, the child's birth weight is too low and there are many health problems, more than 80% of the functions survive for several weeks, and it is rare to live to more than 10 years old.

It can also detect Rh blood type and fetal sex.

The most common noninvasive DNA test calculates all cfDNA, and if the number of chromosomes is correct, it indicates that the risk of having these birth defects is low. On the contrary, the risk is high and further examination is required. Noninvasive DNA is 99 percent accurate for Down syndrome and high for Edwards syndrome, but not 100 percent like chorionic sampling and amniocentesis.

Noninvasive DNA is less accurate for multiple births, obese pregnant women, ectopic pregnancies, pregnant women who are artificially inseminated with eggs donated by others, and those taking some blood-thinning drugs.

Noninvasive DNA test results are normal, no additional tests are required, results are abnormal, chorionic sampling or amniocentesis is also required. If you test for Rh negative, you can rest assured that Rh is positive and the fetus must be closely tested.

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