Researchers say the world is ill-prepared for the global crash in children being born which is set to have a major impact on societies.
The average number of children a woman gives birth to is falling.
In 1950, women were having an average of 4.7 children in their lifetime.
Researchers at the University of Washington's Institute for Health Metrics and Evaluation showed the global fertility rate nearly halved to 2.4 in 2017.
Their study was published in the Lancet and also projects fertility rates will fall below 1.7 by 2100.
Fertility rates are falling because more women have access to education, employment, greater access to contraception and are so are choosing to have fewer children.