Announcing too early?

My husband and I have our bfp with our first and I'm due in May. Both of our parents live 22+ hours away from us and just so happens my mother is going on a trip with her boyfriend to the next state over and we agreed to meet them for the week. My mom has no idea we were TTC and I'm so excited to tell her, but I want to do it in person and this might be my only chance for awhile. Is there a rule of thumb when it comes to announcing? And I have to hope she won't spill the beans until we can get to the in-laws lol