Prolonged labor occurs when labor lasts 20 hours or more for a first-time mother, or 14 hours or more for subsequent births. It can be caused by factors like a large baby, a small pelvis, or issues with uterine contractions. Diagnostic tests include plotting labor progress on a curve and monitoring uterine contractions. Nursing management includes considering a c-section if labor deviates from guidelines, using amniotomy to artificially rupture membranes, and augmenting labor with oxytocin if contractions are inadequate.