help.. need advice

I applied for a new job about 2 months ago.. had an interview.. it's full time with benefits.. mon-friday.. weekends and holidays off and paid.. got offered the spot!!!! :) I'm super excited.. however I just found out that I am pregnant.. only about 4 weeks along. I feel guilty like I should tell them now.. but I also don't want them to change their minds about me based on it either. I know I will have to tell them eventually.. but wondering if I should tell them now.. or wait until I am in my 2nd trimester... help