I'm in your area (obvious with the name I guess) and I am going to a Stanford urological oncologist (Dr. Gill) for a 1.3cm mass on my right kidney. I've been seeing him for about a year and a half, as he is of a mind that we're better off to monitor this lesion for now. He's not certain it is malignant and he doesn't want unnecessarily reduce my kidney function if he doesn't have to.
That being said, I'd either stay with Stanford or, if for whatever reason you're uncomfortable there, I'd go to UCSF. UCSF has one of the best cancer groups in the world with Stanford not all that far behind. You might also want to ask about non-surgical procedures at Stanford. They have been using cryo-ablation techniques for some time now. They use small needles to go through the skin and into the kidney mask where they super-freeze the suspicious matter, thereby killing it. It may be a better option for you given your pregnancy.
As for UCSF, my brother-in-law used there cancer center when he was diagnosed with nasopharangeal (I can never remember how to spell that) cancer. It's a cancer that appears in the back of the nose and throat. It's inoperable, so he had three months of pretty much daily radiation therapy and once-a-month chemo. He's been in complete remission for over five years now.
So, again, either of those two hospitals are going to be very good for you.