Aspirin for high blood pressure

Although dr said my blood pressure was perfectly normal, she wants me to take aspiran daily to prevent high blood pressure which she said could occur after 20 weeks. She said I'm at double risk as I'm overweight and pregnant with twins. I'm hesitant as I don't even take aspirin for myself unless I'm in dying pain. I don't want to expose my children to unnecessary drugs or chemicals. She said it's strictly preventative but I'd rather not unless I know for sure it's necessary. Did anyone else get this prescribed?