http://www.gamesas.com/topic/1525012-updatesfixes-are-comming/
I had this same problem, I built more living quarters and a few minutes later the babies were born.
I have got four dwellers sitting around permanently pregnant now. I was able to move them back to their work stations almost directly after they conceived and knocked down the dorm (the first one you build during the tutorial) with the intent of funnelling invaders directly into the water plant and a quick execution, a few hours later.
Do I need to rebuild the dorm in exactly the same spot? Does it relate instead to total dweller capacity?
Could you share a few more details about what you managed to get work for you, please?
There are many posts to this forum about the problem. So far no one has figured out how to fix it. It's in Bethesda's hands. I really wish there was a fix we could do. I have 3 perm pregnant dwellers; one of them being a legendary. So i'm kind of screwed until a possible fix comes out.