1, both of our couples are normal, and there is no family history, there is no need to do Down’s screening Down’s syndrome is a chromosomal disorder that occurs in the normal population and is random and sporadic. Only about 2% of Down’s children are genetically related, i.e. one of the couple is a carrier of chromosomal translocation, which can lead to the birth of a fetus with trisomy 21, while the remaining 98% of Down’s children are not genetically related. Although the occurrence of Down’s syndrome is related to the advanced age of pregnant women, the probability of pregnant women under 35 years old carrying a fetus with trisomy 1 still exists. Therefore, for mothers-to-be younger than 35 years old, it is still recommended to do Down syndrome screening. We are pregnant with our second child and our first child is normal, so there is no need to do Down’s syndrome screening because the occurrence of chromosomal disorders is random and sporadic, so a normal first child does not mean that the second child is normal. Both the first and second child have the possibility of trisomy 21. The first child is normal, but the second child still needs to be screened for Down’s syndrome. 4. Can 4D ultrasound replace high-throughput screening or amniocentesis? No, it cannot. Because 4D ultrasound is to check the fetus for structural abnormalities, while Down’s syndrome is a chromosome number abnormality, and some Down’s syndrome does not combine with structural abnormalities. Therefore, 4D ultrasound is not a substitute for high-throughput screening or amniocentesis. 5.Why fetal chromosomal abnormalities? Is it related to the flu, fever, medication, X-rays and home renovation during pregnancy? The cause of chromosomal abnormalities is unknown, and it is uncertain whether there is any relationship with colds, fever, medication, X-rays and home renovation during pregnancy.