"It's definitely different than the first time. When they say every pregnancy is different, it really is. Just different symptoms,” she shared. “I feel like this one is just a little harder on my body for some reason. But it's been really good."
While Isaiah is ready for his big brother duties, he is adamant about staying away from one task in particular.
"He says he won't change any poopy diapers though," Underwood said. "I understand, maybe I can change his mind."
The couple -- who tied the knot in 2010 -- are getting ready for their expanding brood by picking out a name and moving into a new home.
"We have picked out a name, but we're keeping that to ourselves right now," Underwood said. "We're fixing to move. I haven't bought anything yet, we still have some of the stuff, cribs and stuff from my son, but we'll figure it out. We're about to move so I'll start buying stuff once we're there. It'd be pointless to buy it and then move it."
Watch the video below for more on the country crooner's growing family: