The main causes of placenta enlargement are multiple pregnancies, previous abortion or history of uterine operation, and fetal dysplasia. 1. Multiple pregnancies: Since more than one fetus exchanges substances with the mother, multiple pregnancies are associated with an enlarged placenta. 2. History of previous abortion or uterine operation: due to the damage to the basal layer of the endometrium, affecting the normal development of the meconium. Therefore, the placenta will be enlarged in order to draw more nutrient area. 3. Fetal dysplasia: if the fetus has obvious malformation, etc., it will also lead to enlargement and thickening of the placenta. If the placenta is too big, placenta praevia will easily occur, and vaginal bleeding will occur in the second trimester of pregnancy without any cause. Therefore, pregnant women who find that the placenta is enlarged should consult with a professional doctor in time to take corresponding professional examination.