I don't know how to tell my parents...

Lately I have only told the news to my siblings that I was pregnant again. They are beyond excited. But my parents on the other hand it's a different story. I havent told them and don't know how to tell them. I know this could go either way with how they will feel about it. Mainly because my pregnancy is 15 months apart from when I had my daughter Serenity. I'm talking to my mom now and want to tell her so bad but I can't. I'm thinking maybe when we find out the sex of the baby to tell them???? (Sigh)