The possible reasons for not being able to breathe in the third trimester of pregnancy include: 1, suffering from more serious anemia, if during pregnancy, improper dietary intake, lack of iron in the body or B vitamins, folic acid deficiency, etc., can easily lead to anemia in pregnant women, anemia symptoms will cause the feeling of not being able to breathe. 2, thyroid disease, if during pregnancy combined with thyroid disease, thyroid nodules, thyroiditis, etc., resulting in enlarged thyroid gland, compression of the respiratory tract will also cause this performance. 3, pregnancy combined with heart disease, before the pregnancy itself has heart disease, no obvious clinical symptoms, after the month of pregnancy with the pressure of the airway, The symptoms of the thyroid gland will also be caused by the enlargement of the thyroid gland and the pressure on the respiratory tract. 3. heart diseases during pregnancy, which have no obvious clinical symptoms before the pregnancy, but after the pregnancy, with the increase of the pregnancy month, the burden on the heart will increase and there will be obvious clinical manifestations. 4. respiratory diseases during pregnancy, such as asthma attacks, bronchitis, laryngitis, etc., may occur. manifestations.