Sudden breast enlargement is commonly caused by the following reasons: First, pregnancy: When a woman is pregnant, the hormone level in her body will be significantly higher, which will cause a significant increase in breast size, you can go to the hospital to improve the relevant tests, such as blood HCG, and uterine adnexal ultrasound for clarification. Second, breast enlargement: when breast enlargement is more serious, the breast can be enlarged, more obvious before the menstrual period, you can go to the hospital to check the breast ultrasound for clarification. If the disease, do not worry too much, go to the hospital regularly to review can. Thirdly, there is a swelling in the breast: it may be benign breast fibroid or malignant breast cancer, which needs to be clarified by mammography or mammography.