So I need advice on how to talk to my mom

I'm fairly young and definitely still dependent on my parents. I'm about to go off to college and I have decided that I want an IUD because really, it's the best option as far as delaying pregnancy and not having to take pills every day. My mom is fairly open-minded, which is why I want to talk to her instead of my dad (who definitely would not approve). However, we rarely talk about these kind of things and I'm a little bit nervous. How should I tell her that I want to have an IUD inserted?

I should probably add that my parents are divorced.

UPDATE: I just left the letter on the dining room table.

UPDATE 2: Success! We're making the appointment now!