If your on bedrest I would suggest a bed bath. Not,a shower or a bath. One tub/bucket soapy one clean water and a few wash clothes. Top to bottom seperate cloths for private areas.
I agree. A sponge bath would be the better option. While the bath itself probably won't cause you to dilate more the added movement may and this early on every day that your baby stays inutero the better.
Being that I'd hate bed baths I'd call on Monday for details on that specific question. Dr knows your individual situation..