The hard lumps in the breasts during pregnancy are considered to be caused by normal physiological phenomena, and may also be considered to be caused by pathological factors, such as mammary fibroadenoma, breast hyperplasia and so on. 1. Physiological factors: hard lumps in the breast during pregnancy may be due to the secretion of a large amount of estrogen, progesterone and prolactin by the embryonic villi, which leads to mammary hyperplasia, and a large amount of breast enlargement within a short period of time, resulting in hard lumps to the touch, which is a normal physiological phenomenon. Generally, after the third month of pregnancy, the hormone level in the body will stabilize and the breast lumps will disappear. 2. Pathological factors: (1) Breast fibroadenoma: it is the most common benign tumor of mixed hyperplasia of breast epithelial tissue and connective tissue in adolescent and childbearing age women, which can lead to breast lumps, pain and other uncomfortable symptoms. (2) Mammary hyperplasia: also known as cystic disease of the breast, is a common benign breast lesion that occurs in women aged 30-50 years old. The cause of the disease is not clearly defined, and it can lead to breast nodules, breast pain, nipple discharge and other uncomfortable symptoms. In the clinic, when there is a hard lump in the breast during pregnancy, it is necessary to go to the hospital in time for diagnosis and identification.