It may be that you won't make 40 weeks because of the potential pre-e, but as far as dilation goes...
My sister was "closed tight as a steel drum" according to her doc, but eighteen hours later, she checked into the hospital at 4cm, 80%.
My best friend was at 2cm, 70% by 37w. Five weeks later, at 42w1d, she ended up with a c-section following two days of labor that never progressed past 6cm.
The more stories I hear, the more it seems that dilation/effacement doesn't mean much until you're 5-1-1.