I just tried Prenatal Yoga here this afternoon- it was great! I would highly recommend it to anyone looking for a yoga class in the South Bay. It's $18 a class, if you're a teacher it's $13 (they have packages as well).
Prenatal Yoga is on Wednesdays at 5:45-7:00pm and Saturdays at 1:00-2:15pm.
I plan on going Saturday and making it a regular class for me.
It's pretty much right at the intersection of Pier Ave and PCH.
Here's the website: http://www.lyfeyogacenter.com/Inside_Lyfe.asp