Fertility rates have fallen dramatically, according to a new study following population trends in every country, the BBC reports.

Researchers were surprised to find that women are having fewer children and half the world's countries may not be able to maintain their populations. This trend could have serious social and economic consequences for nations with more grandparents and elderly people than children.

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While women were having an average of 4.7 children in their lifetime in 1950, fertility rates dropped to 2.4 children by 2017.

But fertility rates vary significantly from country to country.

While women in Uganda, South Sudan, and Somalia have more than five children on average, women in Western and European nations tend to have much lower fertility rates. In the UK, women are having less than two on average, which is below the replacement rate of 2.1 — the number of children needed to maintain the population.

"We've reached this watershed where half of countries have fertility rates below the replacement level, so if nothing happens the populations will decline in those countries," Professor Christopher Murray, the director of the Institute for Health Metrics and Evaluation at the University of Washington told the BBC.

Economically developed nations like many in Europe, the US, South Korea, and Australia are among those that could face demographic disasters in the future. However, the impact of falling fertility rates is yet to be seen since wealthier nations also tend to have longer life expectancies and attract migration.

For many nations across Europe, like Germany Spain, Austria, and Sweden, immigration has been essential to maintaining and growing the population, the Atlas reports.

"Demography impacts on every single aspect of our lives, just look out of your window at the people on the streets, the houses, the traffic, the consumption, it is all driven by demography," Dr. George Leeson, director of the Oxford Institute of Population Ageing told the BBC.

"Everything we plan for is not just driven by the numbers in the population, but also the age structure and that is changing, so fundamentally we haven't got our heads around it," he said.

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Researchers attribute falling fertility rates to fewer child deaths, greater access to contraception, and more women pursuing education and careers — which suggest improvements in healthcare and progress in gender equality.

And a decrease in the human population may benefit the environment considering the rate at which we are exploiting natural resources and causing climate change.

The issue lays in balancing population — ensuring there are enough young people to care for aging folks, and that women around the world have equitable access to healthcare, education, income, and can decide the size of their own families. And compassionate immigration policy is not only needed to support human rights, but it could also boost the population in countries where fertility rates are falling.