A placental thickness between 2.5-5cm at 37 weeks is normal. The placenta is divided into the fetal side and the maternal side. The presence of abnormalities in the placenta can be determined only after careful examination of the placenta after delivery. During pregnancy, only the part of the placenta, maturity and the thickness of the placenta can be seen. A placenta thickness less than 2.5cm should be noted for fetal growth retardation, which may result in full-term low weight babies and also intrauterine infections. In addition, the thin placenta should be suspected of having a membranous placenta, which is characterized by a large and thin placenta area. Second, placenta thickness greater than 5cm 1, systemic diseases: placenta thickening, pay attention to whether the pregnant woman has diabetes and anemia, whether there is abnormal hematoma, interstitial dysplasia and edema in the placenta; 2, placenta abruptio: if the pregnant woman is older and combined with chronic nephritis, or in late pregnancy, there is gestational hypertension, accompanied by significant placenta thickening, to consider that it may be placenta abruptio. Premature placental abruption can cause coagulation dysfunction and renal failure in pregnant women, and may also lead to acute intrauterine distress of the fetus, or even fetal death in the womb, which is a more serious disease. Therefore, once the diagnosis of placental abruption is confirmed, it is recommended to terminate the pregnancy by cesarean section as soon as possible; if the opening of the uterus has been fully opened and the position of the fetal head is low, vaginal delivery is also possible; 3, placental hemangioma: when the placenta is thickened, pay attention to whether there are abnormal hemangiomas in the placenta, if there are placental hemangiomas, pay attention to possible spontaneous bleeding, so pregnant women should try to avoid trauma.