Why doesn't he want to tell his family?

My husband and I have been together for nearly 9 years, almost 2 years married. We moved from MA to FL last October for my new job. He has been a little sad because he misses his family.

We just found out we are going to have a baby a week ago. I have already told my immediate family members and some of my friends after I asked him if that was ok with him. He hasn't told his family yet, wven though he calls them everyday and is very close with them.

I just don't understand it. How can you keep something so exciting like that from your family?

I am not as close to my family as he is to his. I call them every once in a while or skype with them every few weeks, but I still felt it was really important to share that with them.

I really want to understand it, but its making me so sad. I want to tell his sister because I am close with her, but he doesn't want me or him to tell her yet. He said he doesn't want to tell them until maybe May.

I am really trying to understand it. Anyone else's husband hold out from telling his family for a long time? If so, what was his reasoning?