New job & pregnant

I’m 14 weeks pregnant and just got a job offer today. I didn’t tell them during the interview, but i’m just wondering how long I should wait to let them know. It’s part time so I won’t be having maternity leave officially, i’ll just take some time off. It’s an easy job with no heavy lifting or anything I need to be careful of, but I live in an at will state so they can fire me with or without cause. I’m worried that they will be mad I didn’t tell them during my interview but I didn’t want that to effect their decision.