Pregnancy and Birth: Down’s Screening

1. Which is more accurate, the early Tang Dynasty or the middle Tang Dynasty?

As a screening tool, Neither the Early Tang Dynasty nor the Middle Tang Dynasty can be diagnosed. So it’s not accurate, There is no “accuracy”. Usually, [detection rate] and [false positive rate] are used to evaluate a certain screening method. High detection rate and low false positive rate are a good standard for screening methods. Judging from the current situation in China, The detection rate in the early Tang Dynasty is higher than that in the middle Tang Dynasty, and the false positive rate is lower than that in the middle Tang Dynasty. The detection rate in the early Tang Dynasty is about 85%, the false positive rate is about 3%, the detection rate in the middle Tang Dynasty is 65-75%, and the false positive rate is 5-8%.

2. Since Zaotang is more accurate, why don’t many places do it?

In the early Tang Dynasty, NT must be added. The testing of NT requires high technical requirements of ultrasonic doctors and the configuration of ultrasonic machines. We need the best ultrasound equipment and the highest-level ultrasound doctor. There are not many doctors who have really obtained NT certification from the British Fetal Medical Foundation in China. The examination also depends on the baby’s position. If the baby’s position is not good and the best detection plane cannot be obtained, NT measurement is inaccurate. Generally, it takes at least 20 minutes for an NT measurement, so NT detection is the main bottleneck that cannot be carried out on a large scale in the early Tang Dynasty.

3. Do you still need to do the middle Tang after doing the early Tang?

Both the early Tang Dynasty and the middle Tang Dynasty are mainly aimed at screening the risk of Down’s syndrome. According to different screening strategies, the methods are different. If a single screening is conducted, the early Tang Dynasty does not need to be the middle Tang Dynasty. If the joint screening strategy for early and middle pregnancy is adopted, the mid-Tang Dynasty needs to be done after the early Tang Dynasty, and then the joint risk is calculated.

4. The result of Down’s screening is high risk. Since false positives are not low, can I have another review?

The principle of Down’s screening is not to repeat the test, because screening is not a diagnosis, it is a general judgment of risk, and different testing systems will also have different judgments on the same sample. Repeated testing will also bring confusion in interpretation. If the results of the two tests are different, which one should you believe?

5. Since the detection rate in the Middle Tang Dynasty is not high, only about 65%, why should we do it?

Although the detection rate of mid-Tang screening is not satisfactory, if mid-Tang screening is not done and only pregnant women over 35 years old are used as screening methods, the detection rate of Down syndrome is only 30%, so something is better than nothing. Although the detection rate of mid-Tang screening is not as high as everyone expected, it is still much better than not doing screening.

6. Can’t twins be used as Tang sieves?

It is not recommended to assess the Down’s risk of twins solely by maternal serological indicators (such as mid-Tang), but early Down’s screening in combination with ultrasonic markers (including NT, tricuspid regurgitation, etc.) of each fetus and maternal serological indicators during early pregnancy is valuable. The detection rate of NT plus serological screening for twins is 75-80%, and the false positive rate is about 5%.

7. What should I do about ultrasonic soft indexes such as low risk and strong ventricular light spots in Tang Sieve?

Ultrasound should first exclude the presence or absence of fetal structural malformation and other genetic markers. If it is an isolated ultrasonic marker, the risk value of Down’s syndrome should be corrected again according to the likelihood ratio of different ultrasonic soft markers (i.e. Increasing the risk of Down’s syndrome) and background risks to determine whether invasive prenatal diagnosis is needed.

8. What about the critical risks prompted by Down’s screening?

Different screening methods will indicate different risk classifications. Some screening strategies are only divided into low risk and high risk. Invasive prenatal diagnosis (such as amniocentesis) is recommended for high risk. Some screening strategies have critical risks. Joint screening strategies should be considered according to specific conditions or risks should be recalculated according to ultrasonic markers.

9. Do you need amniocentesis if the sugar screen fails?

[sugar screen] and [Tang screen] are different, [sugar screen] is diabetes screening, [Tang screen] is down’s syndrome screening, the latter high risk needs to do amniocentesis, the former did not pass is gestational diabetes mellitus, don’t need to do nourishment. Don’t laugh, clinical really met [sugar screen] did not pass the expectant mother to ask for amniocentesis, really fainted!

At the age of 10. 35, you can’t do Tang sieve. Do you have to do amniocentesis?

35 is a high risk of age, China’s Maternal and Infant Health Care Law stipulates that Pregnant women over 35 years old are advised to undergo direct prenatal diagnosis (such as amniocentesis, etc.) to confirm whether they have children with Down’s syndrome. However, it does not mean that Tang sieve cannot be performed at the age of 35. Older pregnant women fully understand the detection value of Tang screening (i.e. Down screening is a risk assessment, low risk means that the possibility of having Down children is less, but it does not mean that there is no risk.), can still do Tang screening.

11. Our husband and wife are normal and there is no Down’s syndrome in the family. Why should I do Down’s screening?

About 95% of Down’s syndrome patients have normal parents and no Down’s syndrome in their families. Its occurrence is caused by the cell division error in the early stage of fertilized egg or the division error of germ cells (sperm or egg). Only less than 5% of Down’s syndrome is related to the occurrence of parents’ chromosome structure abnormalities (such as translocation). So theoretically, No matter whether there is a family history or not, all pregnant people should be screened for Down’s syndrome, because normal pregnant people are likely to have Down’s syndrome, and the risk of Down’s syndrome for normal pregnant women under 35 is 1/700-1/800.

12. Since Down’s screening is inaccurate and non-invasive fetal DNA testing is more accurate, why not directly replace Down’s screening with non-invasive?

(1) At present, noninvasive fetal DNA detection is only aimed at aneuploidy of chromosomes 21, 13 and 18, while Down’s screening also has certain screening effect on aneuploidy of other chromosomes and some chromosome structural abnormalities;

(2) Some serological indexes in Tang Sieve are related to the occurrence of some pregnancy complications and have early prediction value for pregnancy complications (such as preeclampsia, etc.);

(3) From the perspective of health economics, the current non-invasive fetal DNA testing cost is relatively high and is not suitable to be carried out as a first-line screening method.

13. What is the difference between non-invasive fetal DNA test and sheep wear?

Non-invasive fetal DNA examination is to determine whether there is a dose change (such as increase or deletion) of the above chromosome fragment by measuring the relative content of the DNA target region (such as chromosomes 21, 13 and 18) from the fetus in the maternal peripheral blood, Can’t see all the information of fetal chromosomes. Amniotic fluid cells contain cells that fall off from the fetus. Culturing these exfoliated cells can visually see the chromosome body of the fetus, Can find chromosome number and structural abnormalities. Non-invasive fetal DNA examination currently belongs to Down’s advanced screening. For Down’s syndrome, the detection rate of screening is about 99%, and the false positive rate is less than 1%. Amniocentesis is the gold standard for prenatal diagnosis. Non-invasive cannot replace sheep wear. Amniocentesis is still recommended for high risk of non-invasive results.

Author: Duan Tao

The article was reprinted by Clove Garden authorized by the author.