Maternity leave.

I work in sales and I am due December 26th. I was planning on working as long as I could, hoping to work up until a week before I'm due. But I'm started to feel like maybe I only wanna work two weeks into December. The holidays are crazy in retail and I'm already having a bit of trouble with pain. I'm also probably not going to go back to this job after my maternity leave because I'm currently in school to get certified and will be able to get placed into a job quickly after I give birth and have maternity leave. So I'm wondering if it's really an issue if I leave this job in the beginning of December? I'd like to decide soon so I can let them know and not leave them hanging during the holidays. I don't know what to do!