4D ultrasound is the most advanced ultrasound examination method in the world, although there is no evidence that 4D ultrasound has any harm to the fetus, but for safety reasons, it is recommended to perform 4D ultrasound examination after 14 weeks, 22-24 weeks is the best time for 4D ultrasound examination, during this period, the fetus organs have been developed and the amniotic fluid is moderate, which is the most suitable for observation, this stage is also the best time for the fetus This is also the best time to have a major teratology examination. In most cases, doctors are using two-dimensional ultrasound to do the examination, and the image is post-processed into three-dimensional, four-dimensional is only dynamic three-dimensional, which can better show the fetal state, and the fetal detoxification examination is the same.