The swelling of the chest on the 20th day of IVF may be caused by external stimulation, changes in hormone levels in the body or successful implantation. 1. External stimulation: breast swelling 20 days after in vitro fertilization may be caused by external stimulation of the breasts and damage to the soft tissue of the breasts, which may be accompanied by redness, swelling and pain. 2. Changes in hormone levels: After in vitro fertilization, the level of sex hormones in the body may change, causing stimulation of the mammary glands, causing the patient to experience breast distension for 20 days after in vitro fertilization, but this does not mean that the implantation has been successful. 3. Successful implantation: breast swelling 20 days after IVF transplantation may also be caused by successful implantation, in this case, the body’s HCG level rises significantly will also promote breast development and cause breast swelling symptoms. In this case, a significant increase in the level of HCG in the body will also promote breast development and cause symptoms of breast swelling. 20 days of IVF chest swelling may also be caused by other reasons, we recommend that the patient go to the hospital in time.