Changes in hormone levels during pregnancy can accelerate the disease progression of breast cancer. After breast cancer is diagnosed, the first step should be to stage the disease to clarify whether there are distant metastases. Common metastases of breast cancer are lung, liver and bone. Chest X-ray is considered safe after masking the abdomen to assess the presence of pulmonary metastases, and intrahepatic metastases can be clarified by abdominal ultrasound. For bone metastases, non-enhanced MRI should be used for evaluation of bone metastases during pregnancy because bone ECT may affect fetal bone development.