At the shelter where I volunteer, as long as the pregnant female is very healthy, tests negative for FIV/FeLV, and is very friendly and sociable, we foster them out. Everyone wants well socialized kittens to adopt, and this way we know the kittens are healthy and have been familiar with humans from the day they were born. If there's something wrong with mom, then she's put to sleep, but not just because she's pregnant (she'll be judged the same as any other animal that is dumped. They also do not do abortions - It's all or nothing.
We have a few "specialized" foster moms who will only take pregnant cats. It's a lot of work. And it's really hard to give up the mom and kittens afterwards (that's if you can't keep them, otherwise, adopt them!)
Call your local shelter, or stop in. Ask about fostering a pregnant cat, and let them know why. Ask them if it's possible for you to do so. Ask about talking with other foster parents who have had pregnant females, so you know what to expect. They may even want you to do this as "training", so to speak. Though, believe me, with kitten season coming up, any shelter will be glad you asked!