Down screening and four-dimensional belong to the pregnancy screening test, but there is a big difference between the two, can not be replaced by each other, the main difference lies in the examination method, examination time, examination objectives and other aspects of the different. 1. check way: Down screening is through the pregnant woman in the fasting state blood test, four-dimensional refers to four-dimensional ultrasound, belongs to a kind of ultrasound. 2. Examination time: Down screening is usually performed in the 15th to 20th week of pregnancy, while 4D is usually performed in the 22nd to 28th week of pregnancy. 3. Examination goal: Down screening is mainly to check whether the fetus has Down syndrome, while 4D is mainly to check whether the fetus has abnormal organ development. It is recommended that pregnant women go to the hospital for regular checkups during pregnancy, pay attention to supplementing nutrients, have a reasonable work and rest schedule, and avoid exertion.