How to handle work talk

So my next appointment and ultrasound is next Friday. At that point I'll be 14 weeks and 2 days and I feel it's time to tell my boss. However I'm unsure how to handle the situation. I just started this job Dec. 2 and I really need it right now saving $ for baby, bills, getting what baby needs, etc. However I do plan to leave and not return once I have my baby. I want to be a SAHM. I am not covered by FMLA since I won't meet the work requirements by that time. All I will have saved up is a few vacation days (already used some for stomach bug sickness). I'm unsure of how to handle the convo and if I should tell her "I plan to leave by this date" or if she asks what I plan to do as far as time off if I just tell her "for now my plan is to use whatever vacation time I will have accrued by the time baby comes". The only reason I don't want to tell her about leaving, is bcuz 1 I will be treated differently and 2 the potential of being fired bcuz of it. I am anxious to tell her and just looking for advice or how you handled the situation. Especially if you were new to your job. And btw, my pregnancy was a planned surprise. Meaning we weren't preventing it, but was surprised when we got a positive!