According to the guidelines of the Health and Family Planning Commission, the best time to test noninvasive DNA is 12 weeks of pregnancy - pregnancy (22 weeks + 6 days). If the upper limit of pregnancy has been exceeded (gestational > 22 weeks + 6 days), the risk of testing is increased; too small (gestational age
In addition, noninvasive DNA prenatal testing may also be considered if the following conditions occur during pregnancy:
1. "Tang screening" or imaging screening, such as B ultrasound during pregnancy, shows abnormalities or increased fetal NT values.
2. It is found that the value of a single indicator changes.
3. Placental preposition, placenta low, amniotic fluid or threatened miscarriage are no longer suitable for invasive obstetric examination.
4. Amniocentesis fails.
5. Psychological disorders arising from invasive obstetric examinations.
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