The sharp decline in global fertility rates may lead to a demographic time bomb, with some populations expected to halve by 2100

• A new Lancet study predicts that nearly every country's population will shrink and some will halve by the end of the century because women are having fewer children.
• The trend could lead to a demographic time bomb, where there aren't enough young people to support the economy and aging population.
• Nigeria, however, is expected to experience the reverse trend, becoming the world's second biggest country by 2100.
• The coronavirus pandemic has also affected family planning, with some women delaying pregnancy further but others expected to have unintended pregnancies due to lack of birth control access.

In the next 80 years, almost every country in the world's population will shrink and some of the largest nations' populations will halve, a new Lancet study predicts.

That's because women worldwide are having fewer children. In 1950, the average number of kids a woman had was 4.7. By 2017, it was 2.4. By 2100, the study authors predict, it will fall below 1.7.

And once women have fewer than 2.1 babies each, the population on the whole declines. In fact, the researchers at the University of Washington's Institute for Health Metrics and Evaluation predicted the world's population will max out in in 2064 at 9.7 billion and tumble to 8.8 billion before the century's end.

Paired with an aging population, the result could be a "demographic time bomb," or when there aren't enough young people to support the economy and older generations.

"This study provides governments of all countries an opportunity to start rethinking their policies on migration, workforces, and economic development to address the challenges presented by demographic change," IHME Director Dr. Christopher Murray, who led the research, said in a press release.

The world's dominant powers will shift

The projections — based on data from the Global Burden of Disease Study 2017 to project future global, regional, and national population and methods for forecasting mortality, fertility, and migration — expect 23 countries including Japan and Italy to halve their population by the century's end.

"That is jaw-dropping," Murray told the BBC.

China will come close, the report predicts, and be overtaken by India as the country with the highest population.

But other countries, mainly Nigeria, will experience the reverse trend: The study expects the nation to grow to 791 million people by 2100 and become the second most populous country.

"By the end of the century, the world will be multipolar, with India, Nigeria, China, and the US the dominant powers," he said, with Europe and Asia receding in influence, Dr Richard Horton, the Lancet's editor-in-chief said in the press release. "This will truly be a new world, one we should be preparing for today."

Women are having fewer children for all kinds of reasons

The US in particular has been reporting a steady decline in fertility rates for decades, with 2019 seeing the lowest number of births in 35 years.

The reasons are multifold, but experts say the ongoing "baby bust" seems to be mostly attributable to changing attitudes toward parenthood that are leading more people delay childbearing and have fewer children once they start, if they have children at all.

Teen pregnancies and births have also significantly declined in recent years.

Despite a sign of progress in many ways, the overall trend has long troubled some experts who say the US could suffer a demographic time bomb, which at its most extreme could lead to the eventual extinction of a country's population.

The new report suggests similar fears could be extrapolated worldwide.

"I think it's incredibly hard to think this through and recognize how big a thing this is; it's extraordinary, we'll have to reorganize societies," Murray told the BBC.

He and colleagues encourage liberal immigration policies and caution against responding to declines in ways that could comprise women's "freedom and reproductive rights," the press release says.

The coronavirus pandemic is complicating family planning too

While the report is based on data collected pre-pandemic, it has also affected family planning worldwide.

Many people who need medical help to get pregnant have needed to delay their fertility treatments. Some may not resume their care or may find it's too late once they're ready or able.

Other couples are holding off on conceiving naturally because so much remains unknown about how the virus affects pregnant women and their future children.

On the other hand, the coronavirus has hampered access to birth control and abortions, particularly among disadvantaged communities and in developing countries.

One UN report predicted that for every 6 months of healthcare service disruption in low and middle-income countries, 47 million women will lose access to contraception and 7 million will experience unintended pregnancies.

Maternal and child mortality rates could boom too.

"We cannot afford to look back on the next 10 years as the decade of picking up the pieces and rebuilding trust in the ability of health systems to deliver on essential services for women and children," Mary-Ann Etiebet, the executive director of Merck for Mothers, said during a special WHO briefing. "We need rather to look back on the next 10 years as the decade of accelerating action because we all came together to do this."

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