1. Which is more accurate, Early or Mid-Tang screening?
In fact, as a screening test, neither early nor mid-tang can confirm the diagnosis, so it is not accurate, and there is no such thing as “accuracy rate”. There is no “accuracy rate”. A screening test is usually evaluated by its “detection rate” and “false-positive rate”. A high detection rate and a low false positive rate are the criteria for a good screening tool.
From the current situation in China, the detection rate of early tang is higher than that of middle tang, and the false positive rate is lower than that of middle tang. The detection rate of early tang is about 85%, and the false positive rate is 10%; middle tang can only identify about 45% of affected fetuses, and the false positive rate is 5%.
2. Why don’t many places do it if the early tang is more accurate?
The early screening is based on maternal serum biochemical indicators combined with fetal NT thickness measurement, so medical institutions that can perform the early screening must be qualified to measure NT. However, NT testing requires high technical requirements for ultrasound doctors and ultrasound machine configuration, and not many doctors in China are truly certified by the British Fetal Medicine Foundation for NT.
In addition, the success of the NT test depends on the position of the baby. If the position of the baby is not good, the best detection plane cannot be obtained, and the NT measurement will not be accurate. Many of the images are “unbearable”.
3. Do I need to have a mid-test after having a pre-term test?
Both early and mid-term screening are done mainly for the risk of Down’s syndrome, but the practice varies depending on the screening strategy. If you have a single screening, you don’t need to have a mid-test if you have the early test; if you have a combined screening strategy, you need to have a mid-test after the early test, and then calculate the combined risk.
Recommendation: We advocate not to use the outdated methods of early and mid-tang.
4. The result of Down’s syndrome screening is high risk, since the false positive is not low, can I want to repeat the test again?
The principle of Down’s syndrome screening is not to repeat the test, because screening is not a diagnosis, but a general judgment of the risk level, and different testing systems may have differences in the judgment of the same sample. Repeat testing can also bring confusion in interpretation. If the results of two tests are different, which one should you believe?
Rant: Don’t use the outdated methods of early and mid-tang.
5.Why do you need to do it if the detection rate of the mid-tang test is not high, only about 55%?
Although the detection rate of mid-tang screening is not satisfactory, the detection rate of Down’s syndrome is only 30% if you do not do mid-tang screening and only use the maternal age over 35 years as a screening method. Although the detection rate of Down’s syndrome screening is not as high as people expect, it is still much better than no screening.
6. Is it impossible to do Down’s syndrome screening for twin pregnancies?
It is not recommended to assess the risk of Down’s syndrome in twin pregnancies by maternal serologic indicators alone (e.g. mid-tons), but early screening for Down’s syndrome in early pregnancy combined with ultrasound markers of each fetus (including NT, tricuspid regurgitation, etc.) and maternal serologic indicators is valuable.
Gospel: Prenatal non-invasive DNA testing is currently available to detect pregnant women carrying twins. However, it is only carried out in the prenatal diagnosis department of designated hospitals and requires a special prenatal consultation for twins to determine whether it is suitable for testing using non-invasive genetic testing methods.
7.What should I do if there are soft ultrasound indicators such as strong ventricular dots with low risk of Down screening?
Non-invasive DNA testing
8.What should I do if the Down’s syndrome screening indicates a critical risk?
Non-invasive DNA testing
9.Do I need to do amniocentesis if I don’t pass the sugar screening?
”Sugar screening is a screening for diabetes, while Down screening is a screening for Down’s syndrome. The latter is a high-risk test that requires an amniocentesis, while the former is a gestational diabetes test that does not require a puncture at all. You can not laugh, the clinical encounter “sugar screening” did not pass the mother-to-be to ask to do amniocentesis, really faint!
10.Do I have to do amniocentesis if I can’t do Down screening at the age of 35?
Pregnant women older than 35 years old are recommended to undergo prenatal diagnosis (such as amniocentesis) to confirm whether they are carrying a child with Down’s syndrome. However, it does not mean that you cannot have Down’s syndrome screening at the age of 35. Advanced pregnant women can still have Down’s syndrome screening if they fully understand the value of Down’s syndrome screening (i.e. Down’s syndrome screening is a risk assessment.) After that, you can still do Down screening.
However, I would recommend non-invasive DNA testing.
11. We are a normal couple and there is no Down syndrome in our family, why do I need to be screened for Down syndrome?
About 95% of people with Down’s syndrome have normal parents and no Down’s syndrome in the family. It is caused by an early cell division error in the fertilized egg or an error in the division of the germ cells (sperm or egg). In less than 5% of cases, Down syndrome is associated with an abnormal chromosome structure of the parents (e.g. translocation).
Therefore, theoretically, all pregnancies should be screened for Down’s syndrome, regardless of family history, because all normal pregnancies are at risk of Down’s syndrome, and the risk of Down’s syndrome in normal pregnant women under 35 years old is 1/700 to 1/800.
12. Since Down’s screening is not accurate and non-invasive fetal DNA testing is more accurate, why not just replace Down’s screening with non-invasive?
1) The report of the non-invasive prenatal genetic test mentions chromosomes 21, 18 and 13, but in fact detects all chromosomes with numerical abnormalities. If other chromosomes are found to be problematic, your clinician will notify you.
2) From a health economics perspective, non-invasive fetal DNA testing is currently more costly and too expensive.
Off-topic: If you have the money to buy an iPhone 6, you might as well go for the non-invasive fetal DNA test.
13.What is the difference between non-invasive twin fetal DNA test and amniocentesis?
The non-invasive twin fetal DNA test is performed by collecting 5ml of maternal peripheral blood, extracting all the free DNA from it and sequencing it using the second generation high-throughput sequencing technology. The relative content of the target regions of fetal DNA (such as chromosome 21, 13 and 18) is measured to determine whether there is a change in the dosage of the above chromosome fragments (such as increase or deletion).
Non-invasive technology has been improved in recent years, and the sensitivity and specificity of detecting fetuses (including twins) with trisomy 21, trisomy 18 and trisomy 13 can reach more than 99%, but this does not mean that non-invasive can see all fetal chromosomal information. Currently, non-invasive tests suggesting high-risk pregnant women all need karyotype verification to detect chromosome number, structure and other abnormalities. However, the inability to localize abnormal fetuses is one of the limitations of the application of this technology, so invasive prenatal diagnosis still cannot be replaced.
However, in practice, most twin pregnancies are normal twins, so noninvasive prenatal DNA testing can, to some extent, enable pregnant women to avoid unnecessary invasive prenatal diagnosis. However, until the level of non-invasive testing is mature, prenatal diagnosis of twin fetuses will still be required in all cases of positive non-invasive testing.