I fell against the steering column on a boat from about 3 feet high---direct hit. I waited 6 months before my mammogram because I knew that it would come back abnormal. Even after 6 months a cyst showed up (remnant of that hematoma) even though my breast did not appear bruised...so wait a longer time. Continue to do a self exam though but just know that a hematoma (internal bleeding forming a huge bruise---sometimes not even visible from the outside) is definitely likely to form.