Birth rate
The region of Sub-Saharan Africa has the highest birth rate in the world. As of 2016, Niger, Mali, Uganda, Zambia, and Burundi have the highest birth rates in the world. This is part of the fertility-income paradox, as these countries are very poor, and it may seem counter-intuitive for families there to have so many children. The inverse relationship between income and fertility has been termed a "demographic-economic "paradox"" by the notion that greater means would enable the production of more offspring as suggested by the influential Thomas Malthus.
Infant mortality
Of the 27 most developed countries, the U.S. has the highest Infant Mortality Rate, despite spending much more on health care per capita. Significant racial and socio-economic differences in the United States affect the IMR, in contrast with other developed countries, which have more homogeneous populations. In particular, IMR varies greatly by race in the US. The average IMR for the whole country is therefore not a fair representation of the wide variations that exist between segments of the population. Many theories have been explored as to why these racial differences exist with socio economic factors usually coming out as a reasonable explanation. However, more studies have been conducted around this matter, and the largest advancement is around the idea of stress and how it affects pregnancy.