I've taken some classes at the Motherhood Center (which is Edloe & West Alabama) not too far from med center. It's a nice place and they have lots of pre-natal classes so it's easy to drop in when you can make it.
I've also taken some pre-natal classes at Yoga Collective, which is in Oak Forrest. They have 6-week workshop series on Saturdays. It's far from Pearland but the classes are from 11-1 (something like that) on Saturdays so you have plenty of time to get there (assuming you don't work Saturdays) and it is a nice space.
i know that Yoga Rasa in Clear Lake has prenatal yoga....
Check out Pure Body Studio's prenatal workshop this Sunday.