First, congratulations on the new baby.
Second, a contributing issue is simply that your dog has now hit maturity. Sometimes behaviors come out that weren't evident before. Is he neutered? If not, it may help some even at this age.
Finally, your dog may very well be responding to pregnancy hormones and into protection mode. It isn't uncommon, but needs addressing, as you know. Some of the Nothing In Life is Free programs (K9Deb is excellent: http://k9deb.com/nilif.htm ) can help reset his mentality that it is NOT his job to make decisions about who can visit, your husband's movements, etc. It would be very helpful if you can have him doing all the feeding, most of the petting/grooming/letting in and out when he is home.
Work on the leave it command, and look at me. Practice a LOT at home, then use them when visitors come or you go out if he even thinks about acting up. Mary Woodward's training lessons are so easy to follow it will make you feel faint. http://www.clickerlessons.com/index.htm
I am sure others will respond, but the forum was down a bit so they may not notice the new threads as you have to look in other places now.