The Demographic Transition Model (DTM) describes how birth and death rates change as countries develop economically and socially. The DTM outlines 4 stages of population growth: 1) high birth and death rates with steady population, 2) declining death rate leads to rapid growth, 3) birth rate declines as well but growth remains high, and 4) birth and death rates stabilize with low growth. Reasons for changes include improvements to healthcare, sanitation, women's status and family planning.