Total fertility rates (TFRs) are defined as the estimated number of children born to an unmarried woman throughout her fertile life; data is generally based on the age range of 15 to 50 years. Over a period of 25 years, developed countries show a constant number of children born to only one woman. The data shows that the three developed countries have a TFR of approximately 2. This can be used to describe why the three developed countries have a relatively consistent population pyramid base in 2015. The selected developing countries appear to have comparatively higher TFRs. high in 1991. However, all three countries have shown a steady decline in TFR, with two of the three countries (Brazil and Turkey) showing a reduction to around two children per woman between 1991 and 2015. This places their TFR at the top world ranking and explains the Trends in the age pyramid in 2015 of a declining child population. Nigeria is of particular concern, however, because 1990 data shows that over the course of her life, a Nigerian woman is expected to have 6 to 7 children; Data from 2015 reveals a decline to around 5. These confusing statistics explain the ever-expanding population pyramid figures, as well as why Nigeria's population has shown the fastest population increase among other countries between 1990 and 2015. This ISF analyzes