Announcing marriage and pregnancy

I got engaged in April and found out I was pregnant about a month later. My friends have no idea that I'm pregnant. They also have no idea that my fiancé and I will be getting married in a civil ceremony in just a few weeks. I don't want to keep it a secret but I don't know if I should feel obligated to tell them ahead of time. Can I post it on Facebook?  Should I not post it on Facebook at all?  Again, I am proud to be getting married and proud to be having this baby and I feel like if I don't share things like I normally would I'm attaching some kind of shame to them. Things get a little more complicated because I am trying to wait until my second trimester to tell people and that coincidentally begins the exact day I will be gett married. I've felt really alone as the only person I can discuss this with is my fiancé so any thoughts would help. Thanks.