The standard value of placenta thickness at 13 weeks should be 2.5-3.0 cm. Normally, the thickness of the placenta will not exceed 5 cm, otherwise it will affect the normal development of the fetus. Generally the placenta starts to form around 75 days of pregnancy, but it varies for each individual. The placenta is fully formed in the 3rd-6th months of pregnancy, when the pregnancy is more stable. The maturity of the placenta is mainly divided into four levels: 0, I, II and III. The maturity of the placenta is related to the development time of the fetus, and the longer the pregnancy of the pregnant woman, the higher the maturity of the placenta. The placenta should pay more attention to the maturity rather than the thickness, the thickness of the placenta will mostly have individual differences, if the thickness of the placenta has a little deviation is relatively normal, and if the pregnant woman has intrauterine infection or hemolysis, the placenta will also appear edema and thicken.