Two-dimensional ultrasonography is a commonly used form of pregnancy test, widely used from early to late pregnancy, and is used to check different items in different pregnancy weeks, which can be used to determine when it is the most appropriate to do according to the test items. 1, determine the position of the gestational sac: ultrasonography can be performed in the hospital during the 6-7 weeks of pregnancy, to confirm the position of the gestational sac, to exclude the possibility of ectopic pregnancy, and it can be used for the correction of gestational week. NT examination at 11-13 weeks of pregnancy can determine the thickness of fetal nuchal translucency, which is mainly used to assess the risk rate of congenital hereditary diseases of the fetus, if the test result is greater than 3mm, then it belongs to high risk, and it is necessary to do further examination, such as serum test, non-invasive DNA, amniocentesis and other tests to determine the diagnosis, in order to reduce the birth of defective children; 3, Detectorization examination: done at about 20-24 weeks of pregnancy When performing the examination for malformation, it can show various parts of the fetal organs, and understand whether there are malformations in the fetal head, limbs and the general structure of each organ, but the accuracy is slightly lower than that of 4D ultrasound; 4, pre-delivery examination: 32 weeks of gestation can observe the size of the fetus, amniotic fluid, fetal position and so on, and determine whether there is umbilical cord bypassing the neck, and be able to direct the selection of the mode of delivery. Therefore, during pregnancy, you should complete the relevant examinations on time under the guidance of the doctor to ensure the normal growth and development of the fetus, and take early measures to deal with any abnormalities found.