It's breast cancer.
Those who have a pregnancy before 20 years of age versus those who have a pregnancy after 35 years of age show a 50% reduction in their risk of breast cancer.
http://www.cancer.gov/cancertopics/pdq/prevention/breast/hea...
Those who have a pregnancy before 20 years of age versus those who have a pregnancy after 35 years of age show a 50% reduction in their risk of breast cancer.
http://www.cancer.gov/cancertopics/pdq/prevention/breast/hea...