Telling new boss your pregnant

I had to leave my job at Amazon due to high stress and living heavy boxes all day and I've just started a part time easy going job. I didn't tell him I'm pregnant when he hired me and it will be obvious soon enough.. it's not going to keep me from doing my job but of course when it comes time I'll be leaving to have the baby. Do you think it's something I should have a conversation about? It's the type of job that someone can easily be replaced I don't think it will be a big deal. Also going to school so probably won't be returning after.