Newly Pregnant and Vacation Requests

I'm only 6wks along, but my supervisor wants vacation requests for all of next year. For me that would include all my maternity leave starting june next year, but I'm not ready to tell work that I'm expecting. Since I would probably be moving near the end of my mat leave (hubby is military) I told them "next summer" we'd be leaving. Do you think that's sufficient? Do I need to give them 9 months notice for maternity leave due to a demanding schedule next year?

ETA: I'm hoping to stay with the same company after mat leave, even if not in the same location.