This is something that is hard to fully plan for. Some people use whatever season or holiday is around as a trigger. When I told mine about the first one, I just told him 'oh, by the way, I have a dr. appt tomorrow, so I'll be home a little late..'
My hubby's reaction, even though we'd talked about having kids, wasn't the warm and fuzzy one that I expected. At first he thought I was kidding, playing a joke. When he realized I wasn't he got mad and left... He apologized 2 days later, when he had come to terms with it. He really was glad, etc. but that's my memory.... me standing in the hall as hubby left...So just be prepared for any type of reaction.