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Down syndrome, noninvasive DNA, amniotic fluid, which one should I do?

Release Time | 2020-04-17

There are many medical tests to prevent Down's children, and many expectant mothers struggle with how to choose. Below, let us look at the advantages and disadvantages of each project.

Down's screening

By taking the serum of the expectant mother, the concentration of type A fetal protein (AFP), human chorionic gonadotropin (β-hCG) and free estriol (uE3) in the maternal serum is measured, combined with the expected date of birth, weight, age and blood At the time of gestation, etc., calculate the risk factor for the birth of a congenitally defective fetus.

The best detection time: 15-20 weeks pregnant.

Advantages: economical, safe and convenient, must check items during pregnancy test.
Disadvantages: low detection rate and accuracy (even the most comprehensive early and mid-term screening can only detect 60-80% of children), high false positive rate (Tang screening is high-risk, a large part of the final diagnosis is Not).

Non-invasive DNA testing

By collecting 5mL-10ml of pregnant women's venous blood and extracting free DNA for analysis, it can be accurately obtained for 21-trisomy syndrome (Down's syndrome), 18-trisomy syndrome (Edward's syndrome), 13-trisomy synthesis Sign (Patau's syndrome) risk rate.

The best detection time: 12-26 + 6 weeks pregnant.

Advantages: non-invasive, no risk of miscarriage, high detection rate accuracy (can detect 99.7% of children), low false positive rate (non-invasive and high-risk, the final diagnosis is not very rare).

Disadvantages: high cost (ranging from 2000 to 3000 across the country), detection of chimeric chromosome abnormalities cannot be detected (amniotic fluid puncture if necessary).


Under the guidance of ultrasound, an elongated needle was passed through the belly of the pregnant woman, through the wall of the uterus, into the amniotic fluid cavity, and the amniotic fluid was extracted for comprehensive inspection.

Best test time: 16-24 weeks of pregnancy (varies from person to person).

Advantages: It can detect 46 chromosomes at a time, and can also carry out gene chip and single gene disease detection, and has high accuracy (the gold standard for the diagnosis of chromosomal diseases). It is currently one of the most extensive and accurate prenatal diagnostic techniques.

Disadvantages: there is a certain risk (puncturing the placenta is the most common potential injury), intrauterine infection (which may cause bacteria to be introduced into the amniotic sac during sheep wear and cause problems), and the risk of blood contact between mother and child (the blood of the pregnant mother is Rh negative , Fetal blood will be dangerous when Rh positive); Because this test has a 0.5% chance of causing miscarriage, expectant mothers must choose an authoritative maternity hospital for related tests.

How should moms choose?

Economical mothers: Tang sieve first, non-invasive or amniotic fluid puncture at high risk or accompanied by other risk factors, this combination is low in cost and safe, because the non-invasive joining, the number of prospective mothers of amniotic fluid puncture will be greatly reduced. But this combination will miss about 10% of children with Down's. Suitable for ordinary pregnant mothers without high risk factors, diligent and frugal.
Luxury mother: Do not do Tang Si, do non-invasive DNA testing directly, carry out amniocentesis without non-invasive high risk or accompanied by other risk factors, because of the non-invasive direct application, this combination has high cost and high detection rate, which can detect 99% Children with Down's. The flaw of this combination is that very few children with abnormal chromosome structure will be missed. Suitable for ordinary pregnant mothers without high-risk factors, luxury petty bourgeoisie.

Precise mothers: expectant mothers who are 35 years of age or older and diagnosed with high-risk Down's syndrome (especially those who have abnormal fertility history and family history) should undergo amniocentesis.