A "remarkable" decline in fertility rates around the world is leading to a “baby bust” in many countries including the UK, health experts have warned, meaning that current rates are not now high enough to maintain current population levels.
Since 1950, globally fertility rates - which represent the average number of children a woman delivers over her lifetime - have declined in 91 nations, including the UK, Singapore, Spain, Norway and South Korea.
In order to maintain the current population size, the average number of live births per woman must be 2.1 children.
In the UK, the rate is 1.7 children per woman, while worldwide it has fallen to 2.4 children, down from 4.7 in 1950.
While fertility rates are falling in many western countries, 104 nations worldwide are still seeing population increases due to their high fertility rates (rates above two).
The findings of the the large-scale study have been published in the medical journal, the Lancet.
The lowest rate was in Cyprus where, on average, a woman now gives birth to one child throughout her life, while the highest was in Niger, with a total fertility rate of seven children.
Dr Christopher Murray, director of the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, said: “These statistics represent both a ‘baby boom’ for some nations and a ‘baby bust’ for others.
“The lower rates of women’s fertility clearly reflect not only access to and availability of reproductive health services, but also many women choosing to delay or forgo giving birth, as well as having more opportunities for education and employment.”
He also told the BBC: “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.
“It’s a remarkable transition.
“It’s a surprise even to people like myself, the idea that it’s half the countries in the world will be a huge surprise to people.”
The figures come from the annual Global Burden of Disease study (GBD), which provides estimates for around 280 causes of death, 359 diseases and injuries and 84 risk factors in 195 countries and territories worldwide.
The study is coordinated by the IHME and involves more than 3,500 collaborators from across more than 140 countries and territories.