There's four stages in the classical demographic transition model:
Stage 1 - Pre-transition
In this stage, the birth rates are very high, but also the life expectancy is very low, thus the growth of the population is slow.
Stage 2 - Early transition
In this stage, the birth rates are very high, but the life expectancy is increased, so the population grows rapidly.
Stage 3 - Late transition
In this stage, the birth rates decline slightly, and the life expectancy is a bit higher, thus the population growth is slowing down.
Stage 4 - Post-transition
In this stage, the birth rates are declined significantly, the life expectancy is pretty high, so the population is either growing very slowly, or it is declining.
