During pregnancy, in order to ensure the health of the pregnant mother and the fetus, a lot of examinations are required. Down’s syndrome screening is one of the most important examinations, which can reduce the risk of children with Down’s syndrome. birth rate.
So what is Down syndrome? Down syndrome refers to a congenital abnormality of chromosome 21, and it is also the most common chromosomal abnormality in newborns, with a prevalence of about 1/600.
Most babies with Down syndrome have health problems such as intellectual disability, autism, short stature, heart defects, and intestinal malformations. Although the incidence of this disease is not too high, it will not only bring a great financial burden to children and a family, but also bring greater mental pressure, and some may even overwhelm a family.
And there is currently no effective treatment for Down syndrome. Down screening during pregnancy is the most important preventive measure, so pregnant mothers must do this check.
Down syndrome is primarily caused by chromosomal mutations, which can be caused by many factors, including:
Hereditary factors: Chromosomal mutation diseases are heritable to a certain extent. If one parent is a carrier of a chromosomal abnormality, the risk of the child will be increased by about 10 times.
Older mothers, or exposure to radioactive substances, chemicals, etc. may increase the risk of fetal disease.
Some pregnant mothers will ask, since Down syndrome is related to chromosomes, if both parents have normal chromosomes, is it necessary to do Tang screening?
According to statistics, about 95% of patients with Down syndrome have parents or families without a history of Down syndrome, but it is caused by errors in the early cell division of sperm or eggs or fertilized eggs.
So in terms of prenatal care, all pregnant women should be screened for Down’s syndrome.
At present, Down’s screening is divided into early Down screening and mid Down screening according to the time of pregnancy.
Early Tang screening is usually performed between 9 and 13 weeks of pregnancy, and some are also called “NT” screening, and mid-term screening is usually performed at 15 to 20 weeks of pregnancy.
Down’s screening has certain time limitations. Early or late screening may affect the accuracy of the results. If screening in these two time periods is missed, supplementary screening cannot be performed. Only non-invasive DNA screening or amniocentesis can be performed.
So, is Down’s screening 100% able to detect the problem of the fetus?
Frankly, no.
Down’s screening is for screening, not diagnosis, and screening results are not an exact number, just a ratio. Therefore, the results of Down’s screening can only show the level of risk. Low risk does not mean there is no risk, and high risk does not necessarily mean there must be a problem. In other words, it is very likely that Down’s screening shows a low risk, but it is still possible to have a Tang baby, or that Down’s screening is high risk and the baby is born healthy.
From the current situation of Down’s screening in my country, the detection rate of early Down’s screening is higher than that of mid-stage Down’s screening, but early Down’s screening will be affected by the accuracy of NT color Doppler ultrasound. It cannot be arbitrarily said that the accuracy rate of early Tang sieves is higher than that of middle Tang sieves.
So what if the Down screening results show high risk?
In our country, Tang screening has the principle of non-repetitive examination. The purpose of Tang screening is not to diagnose, but to screen out pregnant women who are more likely to have the disease.
In addition, the test results of Tang screening do not have a specific value, but only a range. If the results of the two screenings are different, it will be more difficult to decide which screening result should be believed.
So during the pregnancy test, if there is a high risk of Tang screening, doctors generally recommend non-invasive DNA screening or amniocentesis.
If the non-invasive or amniocentesis result is still positive, then the pregnancy needs to be terminated to prevent the birth of a fetus with Down syndrome or other chromosomal abnormalities, to achieve prenatal and postnatal care, reduce family and burden on society.
Since the accuracy of Down’s screening is uncertain, why not go straight to non-invasive fetal DNA screening or amniocentesis? This is because:
First, non-invasive fetal DNA screening is only for aneuploidy of chromosomes 21, 13, and 18, while Down’s screening also detects aneuploidy of other chromosomes and some chromosomes Structural abnormalities can be screened.
Secondly, some serum indexes in Tang screening are related to other complications during pregnancy, such as preeclampsia, etc., which also provides help for the early prediction of these complications.
Third, although the accuracy rate of amniocentesis is high and the detection content is relatively comprehensive, it is traumatic and has the 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 relatively high, and it is not suitable as a necessary first-line screening method.