In the previous section, you learnt about uncontrolled fertility and its impact on maternal and child health. Here we will look at the difference between population size and growth, and the link between fertility and population size and growth. 

It is also important to differentiate between population size and the population growth rate. Population size is a measurement of existing population at any point in time, while the population growth rate tells us what is happening to the population regarding whether it is growing, getting smaller, or remaining constant.

• What will happen to population size if a country experiences a high birth rate with a correspondingly high death rate?. This scenario results in a slow increase in population size.
• What will happen to population size if a country experiences a high birth rate with disproportionally low death rates?. High birth rates and disproportionally low death rates result in rapid population growth.
• What will happen to population size if a country experiences both a low birth rate and a low death rate?. The population size will be well controlled and increase only slowly.
• The primary objective of family planning is to achieve this last scenario (a low birth rate, and a low death rate). Why? Because one of the factors that influences population growth is excess fertility.

Rapid population growth in less developed countries is linked to many problems, including poverty, hunger, high infant mortality and inadequate social services and infrastructure (transportation, communication, etc.) Rapid population growth may intensify the hunger problem in the most rapidly growing countries. Population growth can reduce or eliminate food production gains resulting from modernization of farming.

Population pressures may also encourage practices such as over irrigation and overuse of crop lands, which undermine the capacity to feed larger numbers. In some cases, population growth is quite directly related to a social problem because it increases the absolute numbers whose needs must be met.

For example, some less developed countries have made enormous progress in increasing the percentage of children enrolled in school. However, because of population growth during the same period, the number of children who are not enrolled in school also increased because there were insufficient resources to meet the growing need. Similar observations could be made about jobs and employment, housing, sanitation and other human needs such as water supply, transportation, energy requirement, etc.

These problems are compounded when large numbers migrate from rural to urban areas and increase the burden placed on already inadequate supplies and services.