The placenta is gradually formed during the first 11 to 12 weeks of pregnancy. After 12 weeks of pregnancy, the placenta is examined on every ultrasound monitoring. 12~28 weeks is mainly to check the placenta’s position, thickness, the presence of blood sinuses and other abnormalities. After 28 weeks of pregnancy, ultrasound monitoring of the placenta mainly looks at the location and grading of the placenta. In mid-pregnancy, ultrasound suggests that the placenta is low lying, so it is necessary to pay attention to monitoring changes in the position of the placenta. Placenta grading of grade 2 or above indicates that the placenta is mature, and grade 3 indicates that there is a tendency of aging of the placenta. During pregnancy, you should pay attention to regular pregnancy checkups, because each stage of pregnancy checkups are different, so that if there is any abnormality can be detected as early as possible.