We waited to get our Great Dane(Bubba)because we read that they were very jealous dogs. I think it is better to wait untill the baby is born, then get the Dane. When we got Bubba and brought him home I believe he realized that my son was here first and cut down on the jealousy factor. Also bubba became very protective of our son, and they are the best of friends now.
Have you thought about how you will manage with a new baby and a dog? Is this your first baby? do you realise how much time a new baby needs? Please do not even consider getting a new dog to join the family untill the baby is born and you are sure you can cope with a dog. There is no point in taking charge of a new puppy/dog if you think you can just open the kitchen door and kick it into the garden for half an hour to do its business, they need walking ( regularly ) whether its raining, snowing, strong winds or sunny days and they can't always wait till you decide to get up in the morning at 10:00. But whatever you decide to do, please think about it really seriously before you get the dog, would be a great shame if you had to decide to give the dog up for adoption to a new family three months after you got it. Just think about it, you wouldnt give the baby up for adoption and keep the dog...would you?
Personally I would wait. Puppies are just like babies and need a lot of time and attention. They will throw tantrums in the middle of the night, run circles in the house if bored ( what if you want to set the baby on the floor for play time....puppies and dogs don't understand their feet and claws could harm a small child or baby). And, of course they need to be let outside every couple of hours to relieve themselves. Babies also need to eat every couple of hours or more. You will just find yourself stressed and neglecting the needs of the puppy. Wait until after you have the baby.