No, being pregnant is not a cause of breast cancer. Having babies younger, and especially nursing them, are protective of human breasts. Some of the most thorough, accurate, accessible, well documented information on breast cancer prevention I have found on the website: www.bcpinstitute.org. BCP is short for Breast Cancer Prevention. I like the longer pamphlet, and the most recent pamphlets, as well as everything I have seen on the site! I have taken a hundred of each of the Spanish language pamphlets with me to Honduras on a medical mission. They were well received.