Hard lumps in the breasts of pregnant women without pain may be caused by breast fibroma, breast cancer, breast cysts and so on. 1. Breast fibroma: most of them are single lumps with smooth surface, which can be moved easily and are not adhered to the surrounding tissues, usually without pain. 2. Breast cancer: It is a hard, irregularly shaped lump in the breast with unclear edges, and most of them are not accompanied by pain. 3. Breast cyst: mainly manifested as a lump in the breast, usually without pain. It is recommended that pregnant women with hard and painless lumps in their breasts should go to the hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of the doctor, so as to avoid adverse effects on the body due to the delayed condition.