I live in San Francisco, and I have never seen a parking spot reserved for the pregnant or for parents.
I really don't like the lack of consideration a lot of people have for pregnant women, a simmering rage that how dare a pregnant woman take a seat or a parking spot. Being pregnant is for many of us very difficult, and although not all of us are going to be pregnant women, we were all of us at one point fetuses/part of a pregnancy. A little empathy could go a long way, and it's not as though women are normally going to be taking advantage of pregnancy for long, as it's a passing state with very, very few perks and lots and lots of discomforts. Also, not everyone in that state intended to be there (let's not forget that rapes can result in pregnancies; I never assume that a woman intended to get pregnant -- and indeed someone else's family planning is never my business unless it's my husband or someone expecting something from me). I suspect that often the disapproval is sexual in origin -- obviously the woman had sex to become pregnant (I got a lot of teasing when I got pregnant the first time, and I kept thinking, "I'm over 30 and married; this is really silly. It would be shocking and abnormal if I were virginal as a married, middle-aged person!").