The causes of placental insufficiency are multiple: 1. Pregnancy at an overdue stage. Preterm delivery is the most common factor leading to placental aging. The placenta starts to age, degenerate, reduce blood flow and function after about 2 weeks after the due date, at which time the placental material exchange capacity is far from meeting the needs of the growing fetus, which can lead to intrauterine distress and endanger the fetus. 2. Maternal diseases. If a pregnant woman has a history of hypertension, chronic nephritis or diabetes, or if this pregnancy is combined with gestational hypertension syndrome, there will be spasms or sclerosis of the small arteries throughout the body, causing insufficient blood supply to the placenta and impairing its function. If a pregnant woman suffers from heart and lung disease, severe protein deficiency, anemia, fever, use of certain drugs (hexestrol, anti-cancer drugs), or excessive smoking, the maternal blood oxygen content will decrease and the nutrients supplied to the placenta will also decrease, and placental insufficiency will occur. 3. Uterine factors. If a pregnant woman lies on her back for a long time, suffers from uterine fibroids, uterine malformation, etc., which affects the blood supply to the uterus and reduces the blood flow between the chorionic villi, resulting in insufficient blood supply to the placenta. 4, placental factors. Small placenta, early placental abruption, placenta praevia, vascular embolism (fibrous deposition), vasculitis, umbilical cord complications, etc. 5, fetal factors. Such as multiple pregnancy, fetal heart disease, fetal malformation, etc.