Reet the decision should be solely you and your DH's as only you know this dog.
It's a myth that Pitbull's (and Staffy's) have lock jaw. They have strong jaws and because of their breeding, generally don't want to let go when they "lock on", but there's nothing physically stopping them from letting go.
I was raised with Staffies and Jack Russells, and was taught how to interact with dogs, both our own dogs and other people's. We have a staffy now, and have taught her her 'boundary' around H, ie she's allowed a sniff, she's not allowed on his rug etc. We will teach H that dogs can be dangerous and that we need to be careful around them, even when they seem friendly and regardless of their breed.
Perhaps you should wait and see how you feel after your bub is born as your views may change. I don't feel that you should get rid of your dog just because it's a pitbull. You need to do what you feel is right.