Declining fertility rates In order for a population to maintain its size from generation to generation,each woman must give birth to about 2.1 children during her lifetime. This special fertility rate is often called the population replacement fertility rate. In the last few decades,however,the total fertility rate in the developed world has fallen below that level. Bhattacharya,Hyde and Tu-HealthEconomicsBhattacharya, Hyde and Tu – Health Economics Declining fertility rates • In order for a population to maintain its size from generation to generation, each woman must give birth to about 2.1 children during her lifetime. • This special fertility rate is often called the population replacement fertility rate. • In the last few decades, however, the total fertility rate in the developed world has fallen below that level