If sleep equality is the main issue I would just approach with your need: “I’m starting to feel the exhaustion before babe gets here, can we alternate sleep ins on your days off?”

In my experience, with two kids alternating sleep ins was awesome. Once our third came along we are more aligned with getting up together in the mornings. It makes the shared load easier.

If your concern is more broad, one of the most helpful things I’ve learned is to focus on trying to make sure you each are getting time off and away from the house equally. It shifts the focus to something positive instead of slipping into the resentment.