"Notable" decline in fertility rates

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According to researchers, the number of children that women have had in the world has dropped dramatically in the world.

Their report revealed that fertility rates had dropped, which meant that nearly half of the countries were now faced with a "birth collapse", which meant that there was not enough of children to maintain the size of their population.

The researchers said the results were "a huge surprise".

And there would be profound consequences for societies with "more grandparents than grandchildren".

What was the magnitude of the fall?

The study, published in the Lancet, followed trends in all countries from 1950 to 2017.

In 1950, women had an average of 4.7 children in their lifetime. The fertility rate almost halved to 2.4 children per woman last year.

But that masks huge variations between nations.

The fertility rate in Niger, West Africa, is 7.1, but in the Mediterranean island of Cyprus, women have on average one child.

What should be the fertility rate?

When a country's average fertility rate drops below about 2.1, the population finally begins to shrink (this "recession" figure is considerably higher in countries with high infant mortality rates) .

At the beginning of the study, in 1950, no nation was in this position.

• Women over 34 are denied IVF treatment
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Professor Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington, told the BBC: "We have reached this turning point where half of the countries have lower fertility rates At the replacement level, therefore, if nothing happens, populations decline in these countries.

"It's a remarkable transition.

"It's a surprise even for people like me, the idea that it's half of the world's countries will be a huge surprise for people."

Which countries are affected?

The most economically developed countries, including most countries in Europe, the United States, South Korea and Australia, have lower fertility rates.

This does not mean that the number of people living in these countries is decreasing, at least not yet, because the size of the population is a mixture of fertility rate, mortality rate and migration.

It also takes a generation for changes in the fertility rate to materialize.

But Professor Murray said, "We will soon move to a point where societies are struggling with a declining population."

Half of the world's countries still produce enough children to grow up, but as the number of countries progressing in economic terms increases, so will the fertility rate.

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Why does the fertility rate decrease?

The drop in the fertility rate is not due to the sperm count or any of the things that come to your mind when you think about fertility.

Instead, we rely on three key factors:

• Less deaths in childhood, which means that women have fewer babies
• Better access to contraception
• More women in education and work

In many ways, the drop in fertility rates is a success.

What will be the impact?

Without migration, countries will face aging and declining populations.

Dr. George Leeson, director of the Oxford Institute of Population Aging, says this does not have to be a bad thing, as long as society as a whole adjusts to the profound demographic change.

He told the BBC: "Demographics affect every aspect of our lives, just looking out the window at people in the streets, houses, traffic, consumption, everything is dictated by demographics.

"Everything we plan does not only depend on the numbers of the population, but also the age structure and it evolves, so that basically we are not aware of that."

He thinks the workplaces will have to change and that even the idea of ​​retiring at age 68, the current maximum in the UK, will not be sustainable.

The report, which is part of the global burden of disease analysis, indicates that affected countries will need to consider increasing immigration, which can create their own problems, or put in place policies that encourage women to have more children. , which often fail.

According to Professor Murray, author of the report, "According to current trends, there will be very few children and many people over the age of 65 and it is very difficult to maintain global society.

"Think of all the profound social and economic consequences of a society structured in this way with more grandparents than grandchildren.

"I think Japan is very aware of this, it is facing a decline in the population, but I do not think it affects many Western countries because low fertility has been offset by migration.

"But at the global level, there is no migration solution."

What about China?

China has experienced tremendous population growth since 1950, from about half a billion people to 1.4 billion.

But she too faces the challenge of fertility rates, which was only 1.5 in 2017 and has recently moved away from her famous one-child policy.

The reason that developed countries need a fertility rate of 2.1 is that not all children survive until adulthood and so babies have slightly more chances to be men only women.

But in China, the report shows that for every 100 girls born, there were 117 boys, which "implies a very selective abortion based on gender and even the possibility of female infanticide".

This means that more children are needed to have a stable population.

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