If she gets to sleep through the night, she gets to wake early and take care of the child while you get a few hours uninterrupted sleep. Sleep is as important for your mental health and longevity as exercise is for your physical health and longevity.

I am a heavy sleeper too, so the agreement my wife and I had, was that she attend her son at night, he needed to be breastfed anyway, while I got to sleep. Then I was up at an ungodly early time and took care of my son while she could get some uninterrupted sleep. We did this for both of our children.

Her being pregnant is not an argument in favour of you having to do everything at night. Perhaps in the first few weeks while she recover, but after that, it's shared in a reasonable way. She does not get to dictate, but in unison you get to find a happy compromise, which includes enough sleep at regular intervals for both of you.

If you are willing to listen, listen to this: You are well on your way to a roommate situation, the first and biggest step towards a divorce. If you do not correct that course, both of you, that is with all likelihood what will happen. This path of a little bit of resentment many times, is a relationship killer.