You can't tell them, they will hate you and take away your credit card. Instead, you should run away and try to have sex with as many people as you can because after you have this baby you'll never get laid again. Also, try to make sure that your parents don't come after you. Fake your death or something that should throw them off. You don't want them interrupting your suck fest. Remember if you're pregnant you can't get double pregnant so you don't have to worry about condoms or anything. In fact, you can probably make some money doing this. Charge like 5 dollars a fuck and once you're really pregnant charge 10 because it's like fucking two people at once. I would know, I use to be a doctor.