aggression in dog since becoming pregnant

We have a 2 year old rescue dog (not sure of the breed, but likely some kind of hound mix). He has always been super friendly with both dogs and people and loves to play. Since I've become pregnant, he has become aggressive with other dogs on our walks. He's still fine at the dog park and with other dogs at our house. But, when I/or my husband and I are walking him and another dog is approaching he starts to crouch down and get in pounce position, starts barking like crazy, and if we don't stop him, will try to bite/attack other dogs! This is a complete 180 for our sweet pup and I'm really hoping he goes back to his normal self after baby comes. Has anyone else experienced anything like this?