I think you shouldn't have to say anything. Last time I was pregnant I started a job when I was 14 weeks pregnant. They asked me if I could see any reason I wouldn't be able to perform my job duties in the near future and I said nope. As far as I'm concerned I can still perform my job duties after the baby is born. Its none of their business.
I'm starting to look for a new job too, and you should not tell your potential employer of being pregnant until AFTER you accept the position, otherwise you might not get the job if there is someone else there also looking at.
The question you mentioned about performing your duties does not include pregnancy or being put on medical leave. You are healthy (although pregnant), and being pregnant won't effect how you preform your job. I would simply say I didn't see any reason I wouldn't preform my job duties. Unless you plan on not going back to work after having the baby, typically your out for 6-8 weeks. I've had that question in every single interview even when I was in high school interviewing for positions.
With my current job, they actually knew I had a son because when I was laid off I had taken a phone call and the manager that hired me heard my son in the background. Having a kid won't make a difference, but being pregnant will.
I am going to be 11 weeks on Wednesday, and I'm sure I'll have job interviews after the 12 or 13 weeks that I planned on telling people. To help me out, I"m not posting anything anywhere or even telling my current employer until I have secured a Job, or I'm clearly showing. Being pregnant shouldn't effect you getting the job, but in most cases it does, so it's best not to tell.
I recently interviewed for jobs at 9 weeks pregnant. I waited until I was offered the job then went ahead and told my employer about the pregnancy because it is a smaller company and I didn't want her to feel like I was intentionally trying to keep anything from her. I know legally you don't have to say anything, but I decided to be up front and honest from the start, and my boss was completely understanding. I think it totally depends on the job and the company. Best of luck!