Advice/ opinions

Now let me start by saying, the ONLY time I have ever spoken to my boss in person was at my interview. So in the last year we have communicated solely via email. I work nights and she works days. I am pregnant and it is about time to let the boss know since I am starting to show. I am just not sure how to word the email. I was also advised by my doctor to tell the boss in writing so there is proof, apparently my workplace (not my unit) has a bit of bad history of letting people go for unrelated reasons while pregnant, then claiming it was a coincidence. Nothing like a little added stress! I actually get along well with my boss and she seems to genuinely care about us, so I don't think it is my unit that has had the suspicious firings. But just to cover myself, how would you suggest wording the email? I am thinking right to the point. " Just wanted to let you know I am expecting a baby in June" I do plan to work up until then.