Facebook's Timeline is not even universally available, yet, despite being close to one year old. But that doesn't mean Facebook is sitting still. One of the things it's been doing to improve it is to add more event types.
The latest "life event" you can add to your Timeline is "Expecting a Baby" which is probably more interesting and important than events that were available from the get go, like "broke a bone."
"Life Events are easy and expressive ways to mark significant moments in your life such as getting married, buying a house or traveling to new places. If you choose to, you can now share that you are expecting a baby with your friends on Facebook," Facebook explained
Using this is a sure-fire way to make sure all of your friends know about it, if you want to do that, of course. It's also a fair warning to your friends about the deluge of photos and updates to come, perhaps to give them time to install unbaby.me.