When to tell my boss I'm pregnant?

Amy
Okay, so today I am officially 12 weeks pregnant! (Yay!). However, my husband and I have had two previous miscarriages, so we haven't told any one about this pregnancy except family.  Today my school I work for gave out intent letters, asking if we intend to come back for the next school year or not.  I know for a fact if everything works out with this baby I will be a stay at home mom, but if for some reason something bad happens, I would still want to teach.  I live in a SMALL town, and if I say my intent is no- I know I would be asked why.  If I say I'm pregnant, it would get around before my husband and I even get the joy to announce for ourselves.  (We are wanting to wait until beginning of March to announce) however, I have to give my "intent" by Friday... do I say I intend to come back and then in a few weeks change my answer? I feel like that's lying- but at the same time, we have waited a LONG time to announce a viable pregnancy... thanks for any suggestions!