In most cases, at 33 weeks of gestation, the placenta is only at the first level of maturity. If at 33 weeks, the placenta is already at the second level or higher, it is considered possible that the placenta is aging and it is important to observe the fetal condition in the uterus. The placenta is an important organ to maintain the development of the fetus in the uterus. During pregnancy, the placenta secretes various hormones to maintain the pregnancy, delivers oxygen and nutrients to the fetus, and dissolves and purifies the metabolites of the fetus, and is an important organ for material exchange between the fetus and the mother. The maturity of the placenta reflects to some extent the growth and development of the fetus in utero. The ultrasonic grading of placental maturity is one of the important elements of placental function evaluation, and at present, the placenta is mainly classified into four grades, including grade zero, grade one, grade two and grade three, according to the echogenicity and morphology of the placental chorionic plate, placental parenchyma and substrate at all stages of pregnancy. The maturity of the placenta is only one indicator of the placenta, and it also needs to be combined with the position and thickness of the placenta to determine the health status of the placenta. If the placenta is found to be grade 2 or 3 at 33 weeks of pregnancy, it is recommended to do a fetal heart monitoring check and pay attention to whether the fetal heart is normal or not. If the aging of the placenta is accompanied by a bad fetal heartbeat, it suggests the possibility of acute fetal intrauterine distress, while measuring the changes in blood flow, and if the diagnosis of acute fetal intrauterine distress is made, it is necessary to terminate the pregnancy by cesarean section as soon as possible. In addition, it is important to take into account the medical history of the pregnant woman. If hypertensive disorders of pregnancy, fetal growth restriction and placental aging occur at 33 weeks of gestation, they often indicate poor intrauterine condition of the fetus and the pregnancy should be terminated according to medical advice.