I think it sounds completely normal to re-focus your love and attention onto your children when start having them and in some ways not feel quite the same about your pet, although most of us will still love our pets. I changed my attitude towards the two cats I had when I was PG and had my twins - still loving them but re-prioritising my sense of protectiveness and love towards my babies first.
The way we feel about our pets is often like we feel towards our children. I've also heard many examples of people feeling less tolerant of their first child when a new baby comes along.
I think this is all instinctive and designed to make us focus on the most vulnerable in the house.
If you also factor in your feelings about your DHs dog in the first place - it wasn't YOUR dog or choice of dog but his - then maybe it's all exacerbated by this. Maybe it's been a bit like having a step-child who you really try to get along with but don't have quite the same connection with as a step parent (Not speaking from any personal experience BTW).
I also supect that ordinary PG hormones make most of us more intolerant and any feelings are exagerrated.
One solution, as well as what others have suggested, would be to get DH to agree to be the sole carer of his dog - doing all the walks, cleaning up, taking to vets, feeding etc etc. After all, it is HIS dog, not your joint pet really. You could say that once the youngest DC is about 1 or 2, you might be more able to continue the dog care but in the meantime, it's as if he's going to be the single parent of the dog and find ways of managing work and dog care too, perhaps even employing someone else to walk the dog, re-train it etc etc, if he hasn't got time.
I know this might sound drastic but perhaps also only fair? It would be different if you were saying how your own adored pet was ill and needy and yet you couldn't find time/ energy etc to look after it as before, now you're PG with another child already too. Then it might be more about you finding ways, supported by DH and others, to continue caring for your beloved pet.
But this sounds as if it's never felt like your pet at all - but his.
Whilst I can also see a good argument for becoming more involved in the dog and doing the training yourself, my own memory of being PG and then having small babies was that I had no time, energy or feelings left over for caring in the same way for my cats - and they were v low maintenance.
I would completely let yourself off the hook, no matter what you decide to do and don't feel at all guilty. Have a heart-to-heart with DH and explain the situation. I hope and presume that he was the one to clean up aftre the poor dog was ill and replace all carpets etc???
There have been so many posts on this list about not getting a dog until you're really ready for it and it sounds as if you're just not in the space or at the life stage right now to interact with this dog. If you were without children, then I could see a much bigger argument for trying to develop your relationship with the dog but your feelings are boudn to be more caught up in mothering your child and expected baby right now.
Actually, could you even get a dog-sitter/ walker who could mind the dog for a few hrs a day anyway, just like you might get more support/ help with older children if you have a new baby on the way?