pregnancy / promotion??? help!!


just looking for a little bit of advice.

i'm 7 weeks pregnant and me and my husband are delighted after a mc in January at only 4 and a half weeks, trying not to get too excited until we see that first ultrasound but very much easier said than done! :) 

i've just been successful in securing a promotion at work, no contract drawn up or signed yet - as due to low staff in my current area, the training for my new role may be delayed until January, by this time (all going well) i'll be about 20 weeks pregnant. 

my dilemma is, when to tell my employer that i am pregnant and that once the training for this role is complete i'll only actually be in the role for 3 months before going on maternity leave? i'm worried i'll be denied the promotion as on paper, nothing has been signed yet and i'm worried that a contract won't be drawn up until January now with the delay in training. Do i give up and accept this just isn't the time for my dream job? i'd love to train, take on the job for 3 months and then return to the role straight after my maternity leave.

I've seen a few bits online - will add below but not sure how relevant they are if you haven't signed a contract etc? 

any advice or help would be amazing! thanks xxx