There are many times in pregnancy, NT, Down’s syndrome, non-invasive DNA, amniocentesis, three-dimensional or four-dimensional ultrasound, etc. are all detector tests, and different tests require different gestational weeks, as follows. 1. NT: Ultrasound examination of fetal nuchal translucency, if it is too thick, the possibility of fetal anomalies is relatively high, usually between 11 weeks-13 weeks +6 weeks examination. 2. Down’s syndrome: mainly screening for trisomy 21 and neural tube anomalies, performed between 15 and 20 weeks of pregnancy. 3. Non-invasive DNA: mainly screens for risk of trisomy 21, trisomy 18, and trisomy 13, and is performed between 12-22 weeks + 6 days of pregnancy. 4. Amniocentesis: Amniocentesis is required if there is a high risk of Down’s syndrome or non-invasive DNA, and is usually performed at 16-22 weeks of pregnancy. 5. 3D or 4D ultrasound: to detect fetal structural abnormalities, usually performed at 20-24 weeks of pregnancy. Pregnant women should do regular maternity checkups and pay attention to the condition of the fetus.