Obstetric four-dimensional color ultrasound examination: 1. Four-dimensional color ultrasound can be done at any gestational age, but it needs to be emphasized that there is currently controversy about four-dimensional color ultrasound in early pregnancy (before 12 weeks of pregnancy). For safety reasons, it is recommended to perform a fetal four-dimensional color Doppler ultrasound after 20 weeks of pregnancy. 2. After 20 weeks of pregnancy, the fetus\’s limbs and major organs are fully developed. However, at 22-26 weeks of pregnancy, the fetal organs are more fully developed and there is more amniotic fluid, which is suitable for screening for fetal abnormalities. Gynecological four-dimensional color ultrasound examination: 1. Abdominal four-dimensional ultrasound examination is not limited by time. Pregnancy