The 24-week 4D and 30-week 4D are both used to rule out serious structural malformations of the fetus, the difference is mainly the screening focus is different, with the gradual improvement of fetal development, 30-week 4D examination, can find the malformations that are not easy to be found at 24 weeks. 24-week 4D ultrasound is a routine examination, can see the local structure of the fetus, so as to screen for the more serious fetal abnormalities, such as cleft lip, spina bifida, cardiac malformations, brain malformations, etc., can screen out most of the fetal malformations, and can also be used to detect the fetal abnormalities. malformations, brain malformations, etc. It can screen out most of the fetal malformations. However, at this time, the fetus is not yet fully developed, and the detection rate of some subtle structural malformations is lower than that of the 30-week 4-D examination. 4-D ultrasound examination at 30 weeks, when the development of the fetal organs is more complete and can be observed in more detail, the fetal internal organs can be observed again to see if there are malformations that are not manifested in the middle of the pregnancy, or if the position of the fetus is not good in the 24-week examination, and the fetus can not be observed accurately, then it is possible to repeat the examination through the 30-week 4-D examination. 30 weeks 4D examination for review to ensure that the fetus is well developed. During the 4D ultrasound examination, it is recommended that pregnant women wear loose clothing and choose the period when the fetus is active for observation to ensure that the development of the fetus can be clearly observed. If the position of the fetus is not good, you can increase the activity of the fetus by walking, climbing stairs and so on, so as to facilitate the doctor’s observation.