I think there's a couple of things going on
There is probably definite jealousy issues going on
This new bundle is taking away Mom's attention
and I'm mad
This is esp true if your Yorkie was your lap dog
The other thing that might be going on is that your pup might be curious as hell as to what this new thing is that has Mom's and Dad's attention so much
The good thing is that you have lots of time before the baby will be in close proximity to your Yorkie
Of course .... if you think the dog can jump into the baby's crib or playpen you need to separate your dog so that cannot happen
But while you're holding your new born
have your husband show the dog attention and give him treats
try to make the pup know that whenever the baby is around that good things are going to happen
also give the dog the baby's blanket to smell
so he gets used to the new addition to the family
I know it seems scary that the dog might hurt the little one but if you introduce the baby in the right way I think you'll be fine