It is better to do 4D ultrasound in 20-26 weeks of pregnancy. Because in this time period, fetal growth and development to each structure is already basically complete, whether there are obvious structural abnormalities can basically be detected by color ultrasound, especially some large malformation problems, such as anencephaly, single-chambered heart, lethal chondrodysplasia, visceral ectopia, etc., generally can be detected by color ultrasound, especially four-dimensional color ultrasound. After all, four-dimensional ultrasound can see the three-dimensional dynamic changes in the fetus, than ordinary ultrasound can be more clearly see the structure of the fetus, can find a lot of fetal abnormalities, and some will therefore need to be induced as early as possible to try to avoid the birth of a serious malformation of the fetus, so be sure to comply with the doctor’s instructions to do a good job of checking.