Prenatal ultrasound examination, not four-dimensional ultrasound. Prenatal ultrasound generally refers to early pregnancy to determine intrauterine pregnancy and 11 weeks after the fetal NT examination, late pregnancy to observe the placenta, amniotic fluid volume, etc. are prenatal ultrasound examination. Four-dimensional ultrasound is generally subject to 22 weeks to 28 weeks of pregnancy to check, than ordinary prenatal diagnostic ultrasound observation is more clear. At this stage, the fetus is relatively small and the amniotic fluid volume is sufficient, so it can more systematically determine the development of each organ and fetal malformation. In addition, a clearer picture of the fetal face can be formed. Level 3 prenatal ultrasound is not 4D ultrasound, they are not exactly the same. The checkup items are also different, pay attention to regular pregnancy checkups, observe the development of the fetus in the uterine cavity, and intervene in time if there is any abnormality.