How to add my fiancee to my green card application?

I'm going to get married soon and I have a pending I-485 but i have not gone to the interview yet. Can I still include my fiancee in my I-485? Will the immigration officer be suspicious if I suddenly add my fiancee to my application?

to Jeff:

I think you can include your fiancée in your I-485 if you get married before your I-485 is approved. Well… some say it’s better to get married before the interview.

to Jeff:

I'd just take the risk (is there any?) if I were you. If my fiance/soon-to-be husband had to start the whole GC process from scratch, that would be such a headache for both of us