Global fertility rate has halved since 1950, leaving scores of countries including the UK with birth rates below levels needed to maintain population size, new research has found.

The annual Global Burden of Disease Study, published in The Lancet, shows that 91 of 195 nations now have fertility rates below replacement level - currently defined as around 2.1 children per woman - leaving them facing a so-called baby bust.

According to the latest data from the US-based Population Reference Bureau (PRB), the 2018 worldwide total fertility rate is 2.4 births per woman, down from around five in the 1960s.

However, the new study, led by researchers at the University of Washington, found drastic differences between fertility rates across developed and underdeveloped countries.

In Niger, Africa, women are having 7.1 children, on average. At the other end of the scale, in Cyprus the average is only one child per woman, with similar rates in South Korea, Singapore and Taiwan.

Latest figures from the UK Office for National Statistics puts the rate in Britain at 1.76.

In less developed countries, a lower birth rate is cause for celebration, because it indicates fewer children are dying and more opportunities for women outside the home. However, in developed countries, it is a cause for concern.

“The country that’s probably the most concerned about this already is China, where the number of workers is now starting to decline, and that has an immediate effect on economic growth potential,” study author Dr Christopher Murray told CNN.

China’s population has grown by almost a billion since 1950. “But it too is facing the challenge of fertility rates, which stood at only 1.5 in 2017, and has recently moved away from its famous one child policy,” says the BBC.

Meanwhile, South Korea has predicted that its average birth rate is due to fall below one baby per woman this year for the first time ever. Experts have warned that the resulting future shortfalls in healthcare, pensions and economic growth will cause “real problems” for South Korea’s economy and society.

So why are women having fewer babies?

Rather than falling sperm counts, or inability to conceive, experts say one of the key reasons that women are having fewer children is shifting societal expectations.

In South Korea, a “deeply patriarchal society”, the status of women is a “major driver of the trend”, says The Guardian.

With worsening job prospects and rising property prices, “women are getting married and having children later in life, if at all, for fear of being denied promotions and facing discrimination at work”, says the newspaper.

Higher education for women is another “big factor” across the world, says Bloomberg columnist Noah Smith. He suggests that the shift from agriculture to urban living means there is “less incentive for families to have kids to work on farms”, while the cost of raising children tends to be higher in towns and cities.

However, Smith puts a more positive spin on the falling number of children being born in many countries. Although the drop poses regional problems, he says that a birth rate below 2.1 is a “magic level” at which the global population will stabilise and decline, putting an end to fears that “overpopulation is going to swamp the planet”.