Depending on the relationship you have with your parents, it might make it harder. They will probably be disappointed (most parents are) but you've just got to be firm in the choices you make. I can't say they'll come around because some don't, but if it's important to you that they stay involved in you and your future child's lives then stress it to them and they should get over it.
Honestly, these days i swear everywhere i look there is young girls having babies i don't think its as unheard of as it used to be.. meaning i think you have some sort of advantage because it is so common these days. i'd say, tell whichever parent you think will take it easier then maybe together you can tell the other parent. i guess i don't know how supportive your parents are but i promise they'll get over it.