I had it happen to me for the first time a little over 2 years ago. I was soooooo excited when I found out my Sis was pregnant! And when she finally had the baby, I was just beside myself. I mean, that tiny little thing was related to ME!
And of course she takes after Auntie Jackie (my temper, my stubbornness, my fierce independance, etc..... Oh, sure, my Sis says she gets it from her Dad, but I know better...

)
It's a very cool thing for you - Congratulations!