I was in a simliar situation, but was 6 months pregnant. I know others have said not to 'lie', but when I was upfront about my pregnancy during an interview, I wasn't called back for a 2nd. The interviewer told me to never reveal that you're pregnant during an interview. It's illegal to fire someone for being pregnant, but there's nothing to prevent them from discriminating in a job interview. They'll just say you weren't a good fit.
On my next interview, I didn't 'lie', but didn't reveal I was pregnant. I needed insurance. My husband couldn't even buy insurance because I was pregnant and that was a pre-existing condition (if a father would have to put a baby on his plan, the insurance company wanted nothing to do with either). I had to protect my family, so I didn't mention the pregnancy until right after I got the offer.
Really, what's 6 or 8 weeks with unpaid leave to them? If you are dedicated before you deliver and after your short leave, it doesn't make a difference in the long run.
Also, 9 years after my first pregnancy, I found a new job and got pregnant 2 weeks after I started that job. Life doesn't run like a movie and it never will. Don't listen to people who tell you to be 'upfront'. You're not there to talk about babies or marriage or things you'd discuss at lunch with the ladies. If your job doesn't involve your personal life (which I'm sure it doesn't), then that topic doesn't belong in an interview.
My employers at both jobs weren't enthusiastic that I was pregnant so soon into my employment, but I did a good job and caught on quickly.
Do what's right for you, but I wouldn't reveal anything about your personal life at any point in the interview process. If you get the job, accept it and then inform them that you'll need to take off x number of unpaid leave in the fall or whenever. I qualified for short term disability after working in my job for only 6 weeks, but it was only a hundred dollars a week.
Good luck with your interview. If you want to chat offline, feel free to drop me a line.