Q. My best friend has been struggling to have a baby for two years, and I just found out I'm pregnant! I'm afraid to tell her. Should I have a mutual friend "let it slip"?
A. Definitely. That way, when your "best" friend finds out, she'll not only feel reproductively inadequate, but completely unworthy of your respect and friendship. Wait. That's probably not the result you're going for.
What you want, I assume, is to avoid hurting your best buddy, right? In that case, you need to gather your courage and spill the beans yourself.
If you chicken out, your friend will never forget that you didn't have the guts to share your news, and you'll never shake the feeling that you let her down.
The question then is how to tell your friend. It will take sensitivity. For instance, make your announcement when no one else is around, so that she doesn't have to put on a brave face. You may consider telling her over the phone, which would allow her to hide her emotions and quickly wrap up the conversation.
Tell her that you have some news (not "big" or "exciting" news. Just news). After you drop the bombshell, add that you don't expect her to jump for joy. Likewise, let her know that you consider her friendship so important that you would never hide something like this.
There's no way around it: This conversation will take you down a bumpy path, but it's the only one you should take. Your friend, and your friendship, is probably stronger than you think. In any case, if she is your best friend, you can be fairly certain that she will be happy for you. Eventually.