Wait until you feel comfortable telling them. Show them how hard of a worker you are and everything will be fine
I got a new job when I was about 12 weeks and I didn't tell them. I never said anything, they just finally asked when I started showing. Around 24 weeks. They weren't upset at all.
I hid my pregnancy at my part time lol. Just tell them. They can't fire you.
Just keep your head up. And proudly tell them your pregnant when you feel ready! If your a good worker they will have no reason not to let you go fulltime other than the fact that your pregnant and that is discrimination and a huge lawsuit that im sure no bank wants!! Be happy enjoy your pregnancy and new job. ^_^