RE: Hey Briee . . .
Yes, the cussing factor is NOT appropriate for Munchkin Land! IMHO, push-ups will leave you somewhat winded, but that is your cue to rest at the top of the push-up and take a deep breath. Because the pec, tri and anterior delt muscles are indeed somewhat smaller in relation to the leg and back muscles, they get tapped out for energy much more quickly, and you need a deep breath or two to load the lungs with oxygen which can then be transported to those working muscles. Obviously, the exertion will expend calories, but again cardiovascular benefit is not what push-ups are all about.
I'm in awe that you're able to maintain your workouts and your push-ups challenge with your new little miracle on the way. From the relatively little that I know about the physiological aspects of pregnancy your body is in total-workout-mode already just making Miracle #6. Congratulations!
A-jock