The Laguna Beach alum also revealed that she has gained 36 lbs. during her pregnancy, currently weighing in at 145.8 lbs.
"We had to stop at a store and I got a little preemie outfit in case he comes early," Heidi said. "He is coming early, I just hope not too early."
"He's not coming early," Spencer relied. "Stay in that belly, boy!"
The pair met on MTV's The Hills and tied the knot in 2009. Hear more on them in the video below.