I agree with PP - it's hard to actually drink one full glass on your wedding day. I wasn't pg, but asked the function co-ordinator to make sure I had mineral water - I didn't want to drink too much and wanted to stay hydrayted. I kept putting down drinks and forgetting about them.

Take a sip of champers for toasts etc, but otherwise stick to soft drink. When people ask, just say you're alternating your drinks. You'll be so busy moving from one person to the next no-one should notice.