Four-dimensional refers to four-dimensional color ultrasound, 20 weeks pregnant can be four-dimensional examination, each pregnant woman has individual differences. If the four-dimensional ultrasound examination is carried out at 20 weeks of pregnancy, it can accurately check the development of fetal organs and systems, and the image display is clearer, at this time 20 weeks of pregnancy can do four-dimensional ultrasound. However, some organs are not well developed at 20 weeks of pregnancy and may be missed or misdiagnosed. For example, if you check the heart, it is smaller at 20 weeks, and sometimes the congenital heart disease is easy to be overlooked or missed. Brain structure is more complex, if the 4D ultrasound examination is performed too early, abnormalities in the ventricles as well as widening of the lateral ventricles may not be easily detected. It is recommended to observe for the time being for two weeks before checking the 4D ultrasound. Now you need to pay attention to rest, observe the fetal movement, and consult the doctor if you find any abnormality.