Do I need to tell my interviewer I'm pregnant?

I am currently unemployed, not married or living with the father of the child and 4 months pregnant. I was employed for over 10 years at the same company but was laid off last year. My dilemna is I am now interviewing for a position for my dream job at a large corporation. I have not told the potential employer I am pregnant as I truly believe I will not be offered the job then. If I am hired my plan was to tell the employer after working there that I truly did not want anything to ruin my chances of being hired. Besides that being the truth I need this job as I have been looking for six months. I do not want to ruin the future relationship with my manager-to-be as I plan to take only six weeks off and I also plan to be working there for years to come. What advice do you have as to how and when to break the news?