In order to ensure the health of pregnant mothers and fetuses during pregnancy, many tests should be done, and Down's screening is one of the most important tests, which can reduce the birth rate of children with Down syndrome.
So what is Down syndrome? Down syndrome refers to a disorder born with chromosome 21 and is the most common chromosomal abnormality in newborns, with a prevalence of about 1 in 600.
Most of the Down babies have mental disabilities, autism, short stature, heart defects, intestinal malformations and other health problems. Although the incidence of this disease is not too high, for children and a family, it will not only bring a great financial burden, but also greater mental pressure, and some will even crush a family.
And there is no effective way to treat Down syndrome at present, and tang screening during pregnancy is the most important preventive measure, so this test must be done for pregnant mothers.
Down syndrome is mainly caused by chromosomal variation, and there are many factors that cause chromosomal variation, including:
Genetic factors: Chromosomal mutations have a certain heritability, if one parent is a carrier of chromosomal abnormalities, the risk of disease in their children will increase by about 10 times.
Maternal age, or exposure to radioactive substances, chemicals, etc., may increase the risk of fetal disease.
Some pregnant mothers have to ask, since Down syndrome is related to chromosomes, if the chromosomes of both parents are normal, is it still necessary to do Tang screening?
According to statistics, about 95% of the parents or families of people with Down syndrome do not have a history of Down syndrome, but are caused by sperm or eggs or early cell division errors in the fertilized egg.
Therefore, from the perspective of eugenics, all pregnant women should be screened for Down's.
At present, Down screening is divided into early Tang screening and mid-tang screening according to the time of pregnancy.
Early Tang screening is usually carried out at 9 to 13 weeks of pregnancy, some also call it "NT" screening, and the second tang screening is usually carried out at 15 to 20 weeks of pregnancy.
Down's screening has certain time limitations, early or postponed, may affect the accuracy of the results, if you miss these two time periods of screening, it is impossible to perform supplementary tests, only non-invasive DNA screening or amniocentesis.
So, is Down's screening 100% able to detect the problem of the fetus?
Frankly, not.
The purpose of Down's screening is screening, not diagnosis, and the screening results are not an accurate number, just a ratio. Therefore, the results of Down's screening can only show the level of risk. Low risk does not mean that there is no risk, and high risk does not necessarily mean that there must be a problem. That is to say, it is likely that Down screening shows low risk, but it is still possible to give birth to a Tang baby, or Down screening is high risk, but the baby is born healthy.
Judging from the current situation of Tang screening in the mainland, the detection rate of early Tang sieves is higher than that of mid-term Tang sieves, but early Tang sieves will be affected by the accuracy of NT color ultrasound, so it cannot be arbitrarily said that the accuracy of early Tang sieves is higher than that of mid-term Tang sieves.
So what if the results of Down's screening show high risk?
In the mainland, Tang screening has the principle of not repeating the examination, and the purpose of Tang screening is not to confirm the diagnosis, but to screen out pregnant women with a high probability of illness.
In addition, the results of tang screening have no specific values, just a range, if the results of the two screenings are different, it will be more difficult to decide which screening results should be trusted.
Therefore, in the process of pregnancy testing, if there is a high risk of Tang screening, doctors will generally recommend non-invasive DNA screening or amniocentesis.
If the result of non-invasive or amniocentesis is still positive, then it is necessary to terminate the pregnancy, prevent the birth of a fetus with Down syndrome or other chromosomal abnormalities, achieve eugenics, and reduce the burden on families and society.
Since the accuracy of Down's screening is uncertain, why not go straight to noninvasive fetal DNA screening or amniocentesis? This is because:
First, noninvasive fetal DNA screening is only for aneuploidy of chromosomes 21, 13 and 18, while Down's screening also has a screening effect on the aneuploidy of other chromosomes and some chromosomes.
Second, some serum indicators in the Tang sieve are associated with other complications during pregnancy, such as preeclampsia, which also provides help for the early prediction of these complications.
Third, although the accuracy rate of amniocentesis is very high and the detection content is relatively comprehensive, it is traumatic and there will be a risk of miscarriage and infection, so amniocentesis cannot be used as a census method.
Fourth, from an economic point of view, the current cost of non-invasive fetal DNA screening is high, and it is not suitable as a necessary first-line screening method.