What would you do?

I am a stay at home wife, my husband is the one who works, well i talk to my husband last night about getting a job, just to make some extra cash for baby stuff, or somthing and for me to get out of the house some. Well i have a interview next friday, and i will be 18 weeks pregnant on the interview date, i want to tell them during the interview i am prenant but i really want the job. It is possible for them to turn me down because i am pregnant, but obviously will not tell me that, but then again i want to wait until i get the job and then tell them but idk. I am leaning twards telling them i can do everything at that job then i could if i was not pregnant. It is a cashier job. What do you think?