Four-dimensional macroanalysis does not say when the best, pregnancy 20-28 weeks can do four-dimensional ultrasound, it is recommended that pregnancy 24-26 weeks to do four-dimensional ultrasound is better. After pregnancy, it is recommended that every woman should go to the hospital to do four-dimensional ultrasound examination, through the examination to be able to fetal basic conditions, such as the size of the fetus, the location of the placenta, the amount of amniotic fluid and other conditions. It is also able to find out if there are any malformations in the fetal head and neck, thorax, abdomen, spine, limbs, nose, lips, and can check for structural abnormalities, but cannot rule out diseases in hearing, vision, intelligence, metabolism, etc. The stage of 20-28 weeks of pregnancy can go to do four-dimensional ultrasound examination, 24-26 weeks of pregnancy examination will be better, at this time the fetus in the uterus development is more complete, the amount of intrauterine amniotic fluid is more moderate, the results of the examination is more accurate, the examination of abnormalities can be dealt with before the 28th week of pregnancy, and try to avoid the 28th week after the induced abortion. The four-dimensional ultrasound has a detection time, should not be too early or too late, so as not to affect the results of the test.