If you're a person who has been pregnant before, you might not be able to do a platelet donation. People who have been pregnant can have HLA antibodies that can cause complications to the receiver of a donation. I know when I wanted to donate platelets, they wouldn't take mine because of my pregnancies - the testing for HLA at the time was cost-prohibitive, so in my area they only take platelet donors who are female with no pregnancy history or male. I just donate whole blood.