There are many reasons why breast lumps are large during pregnancy, such as the following:1. Mastoid hyperplasia is a hormone-related disease, and hormonal fluctuations in the body are more pronounced during pregnancy, which can lead to the aggravation of mastoid hyperplasia, which does not require treatment, so you can wear loose bras, eat more fruits and vegetables, and have regular checkups.2. Breast lymph nodes, if there is inflammation, can lead to lymph node enlargement, and it will also be painful when inflammation stimulation is obvious and there is a certain amount of activity. You can eat a light diet, balanced nutrition, and then treat it after delivery.3. Breast fibromatosis, if it doesn’t affect your life, you can leave it alone and consider surgery to remove it after the breastfeeding period. If it is too big, surgery can be performed in the middle of pregnancy.4. Breast cancer, if diagnosed as cancer, you need to be psychologically prepared for timely surgery and decide to abort according to the situation.