2D ultrasound examination is a more common examination method in pregnancy test, which is widely used from early to late pregnancy, and it is used to check different items in different pregnancy weeks, so you can judge when it is most appropriate to do it according to the examination items. 1. determine the location of the pregnancy sac: you can go to the hospital in 6-7 weeks of pregnancy to confirm the location of the pregnancy sac through ultrasound examination to exclude the possibility of ectopic pregnancy, and it can also be used to correct the pregnancy week; 2. NT test can be done at 11-13 weeks of pregnancy to determine the thickness of the transparent layer of the fetal neck, which is mainly used to assess the risk rate of the fetus suffering from congenital hereditary diseases; if the test result is greater than 3mm, it is high risk and further tests such as serum testing, non-invasive DNA, amniocentesis and other tests are needed to determine the diagnosis to reduce the birth of defective children; 3.Retrogramming test: done around 20-24 weeks of pregnancy When performing the screening examination, it can show the fetal organs in various parts and understand whether there are deformities 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: the fetal size, amniotic fluid and fetal position can be observed at 32 weeks of pregnancy to determine whether the umbilical cord is round the neck and can guide the choice of delivery method. Therefore, we should improve the relevant examinations on time under the guidance of doctors during pregnancy to ensure the normal growth and development of the fetus and take early treatment measures when abnormalities are found.