
Since I have triplets that just turned 4 years old, and four Ridgebacks, I think I am pretty qualified to answer.

The younger the dog, the easier it will be. My dogs were 5 and 6 when the babies were born, and it was a difficult transition. Granted, I had three babies at once, and the activity level in the house went from no one home all day to a house filled with shifts of grandparents and babysitters. It took them about a year to totally adjust.
My bitch was better than my male -- she would just flee if you showed her a baby. My male was really freaked out at the idea of being too close to them, and we had to use a lot of classic conditioning -- food rewards and praise -- to get him to understand they were not alien beings invading his planet to perform scientific experiments on him.
Yes, they know you are pregnant because they can smell the hormone changes and the different way you move your body as pregnancy progresses and, yes, it freaks them out.
It just takes time. Once the older Ridgeback understands that the baby is YOURS, and by extension, HIS, he will adjust, just as mine did.
Today, I might walk into the living room to see two kids sitting (or standing) atop of Blitz while he is curled up on the couch in their favorite TV-watching spot.
Denise