Something about becoming a mom teaches you to throw your plans out the window. ;-)
I worked the day I delivered my first--she came at 37 weeks, to the day--and survived. My journal entries from that time are really short and filled with information about my aches and pains.
With my second, I stopped working early. I was planning to stop 2 weeks early, as insurance generally allows, but ended up going out even earlier for preterm labor issues. My journal entries from that time are filled with information about my life and chronicles my changing relationships.
This is what I believe:
Stopping work forces you to consider the change in your life's pattern. I found that I had more time to reflect on the transition to motherhood and prepare myself mentally for the task of labor. You learn how to take naps, how to listen to your body, how to nourish it properly and deal with the discomforts that are inevitable in the 3rd trimester. I believe the time off really helped me in birthing and in the weeks directly after. Post-delivery with my first (a 6 hour unmedicated affair in a birth center), I was slow to stop bleeding, regain strength, and fall into a routine as a mother. With the second, I could stand and walk unassisted almost right after the birth (which took only 2 hours, unmedicated, at home).
You only go through this change from woman to mother once. Why not enjoy it?