Today, globally, women of childbearing age have an average of approximately 2.2 children over the course of their lifetime. In pre-industrial times, most women could expect to have somewhere between five and ten live births throughout their lifetime; however, the demographic transition then sees fertility rates fall significantly. Looking ahead, it is believed that the global fertility rate will fall below replacement level in the 2050s, which will eventually lead to population decline when life expectancy plateaus. Recent decades Between the 1950s and 1970s, the global fertility rate was roughly five children per woman - this was partly due to the post-WWII baby boom in many countries, on top of already-high rates in less-developed countries. The drop around 1960 can be attributed to China's "Great Leap Forward", where famine and disease in the world's most populous country saw the global fertility rate drop by roughly 0.5 children per woman. Between the 1970s and today, fertility rates fell consistently, although the rate of decline noticeably slowed as the baby boomer generation then began having their own children. Replacement level fertility Replacement level fertility, i.e. the number of children born per woman that a population needs for long-term stability, is approximately 2.1 children per woman. Populations may continue to grow naturally despite below-replacement level fertility, due to reduced mortality and increased life expectancy, however, these will plateau with time and then population decline will occur. It is believed that the global fertility rate will drop below replacement level in the mid-2050s, although improvements in healthcare and living standards will see population growth continue into the 2080s when the global population will then start falling.

The total fertility rate of the world has dropped from around 5 children per woman in 1950, to 2.2 children per woman in 2025, which means that women today are having fewer than half the number of children that women did 75 years ago. Replacement level fertility This change has come as a result of the global demographic transition, and is influenced by factors such as the significant reduction in infant and child mortality, reduced number of child marriages, increased educational and vocational opportunities for women, and the increased efficacy and availability of contraception. While this change has become synonymous with societal progress, it does have wide-reaching demographic impact - if the global average falls below replacement level (roughly 2.1 children per woman), as is expected to happen in the 2050s, then this will lead to long-term population decline on a global scale. Regional variations When broken down by continent, Africa is the only region with a fertility rate above the global average, and, alongside Oceania, it is the only region with a fertility rate above replacement level. Until the 1980s, the average woman in Africa could expect to have 6-7 children over the course of their lifetime, and there are still several countries in Africa where women can still expect to have 5 or more children in 2025. Historically, Europe has had the lowest fertility rates in the world over the past century, falling below replacement level in 1975. Europe's population has grown through a combination of migration and increasing life expectancy, however even high immigration rates could not prevent its population from going into decline in 2021.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In the United States in 1800, the average woman of childbearing age would have seven children over the course of their lifetime. As factors such as technology, hygiene, medicine and education improved, women were having fewer children than before, reaching just two children per woman in 1940. This changed quite dramatically in the aftermath of the Second World War, rising sharply to over 3.5 children per woman in 1960 (children born between 1946 and 1964 are nowadays known as the 'Baby Boomer' generation, and they make up roughly twenty percent of todays US population). Due to the end of the baby boom and increased access to contraception, fertility reached it's lowest point in the US in 1980, where it was just 1.77. It did however rise to over two children per woman between 1995 and 2010, although it is expected to drop again by 2020, to just 1.78.

In the United States, the crude birth rate in 1800 was 48.3 live births per thousand people, meaning that 4.8 percent of the population had been born in that year. Between 1815 and 1825 the crude birth rate jumped from 46.5 to 54.7 (possibly due to Florida becoming a part of the US, but this is unclear), but from this point until the Second World War the crude birth rate dropped gradually, reaching 19.2 in 1935. Through the 1940s, 50s and 60s the US experienced it's baby boom, and the birth rate reached 24.1 in 1955, before dropping again until 1980. From the 1980s until today the birth rate's decline has slowed, and is expected to reach twelve in 2020, meaning that just over 1 percent of the population will be born in 2020.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In 1900, Mexican women of childbearing age would go on to have approximately 6.8 children on average over the course of their lifetime, however this number dropped to 5.6 by 1920, partly because of the Mexican Revolution (1910-1920). The fertility rate increased again over the course of the next sixty years, reaching 6.8 in the 1950s and 1960s, during the worldwide baby boom. However, Mexico's fertility rate has been decreasing steadily since 1970, and is expected to reach it's lowest figure ever in 2020, where the fertility rate will be 2.1 children per woman.

The fertility rate of a country is the average number of children that women from that country would have throughout their reproductive years. In the United Kingdom in 1800, the average woman of childbearing age would have five children over the course of their lifetime. Over the next 35 years the fertility rate was quite sporadic, rising to over 5.5 in the 1810s and 1820s, then dropping to 4.9 by 1835. This was during and after the Napoleonic Wars and the War of 1812 with the US, which was a time of increased industrialization, economic depression and high unemployment after the war. As things became more stable, and the 'Pax Britannica' (a period of relative, international peace and economic prosperity for the British Empire) came into full effect, the fertility rate plateaued until 1880, before dropping gradually until the First World War. The fertility rate then jumped from 2.6 to 3.1 children per woman between 1915 and 1920, as many men returned from the war. It then resumed it's previous trajectory in the interwar years, before increasing yet again after the war (albeit, for a much longer time than after WWI), in what is known as the 'Baby Boom'. Like the US, the Baby Boom lasted until around 1980, where it then fell to 1.7 children per woman, and it has remained around this number (between 1.66 and 1.87) since then.

BackgroundKawasaki disease (KD) is a common cause of acquired paediatric heart disease in developed countries. KD was first identified in the 1960s in Japan, and has been steadily increasing since it was first reported. The aetiology of KD has not been defined, but is assumed to be infection-related. The present study sought to identify the factor(s) that mediate the geographical variation and chronological increase of KD in Japan.Methods and FindingsBased upon data reported between 1979 and 2010 from all 47 prefectures in Japan, the incidence and mean patient age at the onset of KD were estimated. Using spatial and time-series analyses, incidence and mean age were regressed against climatic/socioeconomic variables. Both incidence and mean age of KD were inversely correlated with the total fertility rate (TFR; i.e., the number of children that would be born to one woman). The extrapolation of a time-series regressive model suggested that KD emerged in the 1960s because of a dramatic decrease in TFR in the 1940s through the 1950s.ConclusionsMean patient age is an inverse surrogate for the hazard of contracting the aetiologic agent. Therefore, the observed negative correlation between mean patient age and TFR suggests that a higher TFR is associated with KD transmission. This relationship may be because a higher TFR facilitates sibling-to-sibling transmission. Additionally, the observed inverse correlation between incidence and TFR implies a paradoxical “negative” correlation between the incidence and the hazard of contracting the aetiologic agent. It was hypothesized that a decreasing TFR resulted in a reduced hazard of contracting the agent for KD, thereby increasing KD incidence.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In the second half of the nineteenth century in Spain, the fertility rate fluctuated, but overall it had decreased from 5.1 children per woman in 1850 to 4.7 in 1905. From 1905 until 1935 the fertility decline followed a steady trajectory, falling from 4.7 to 3.5 births per woman during this time. Between 1935 and 1940, the Spanish Civil War caused the fertility rate to drop by 0.7 children per woman. The rate dropped again in the 1940s and 50s, before Spain experienced a baby boom, much like the rest of Western Europe, in the mid 1900s. Compared with the rest of Europe, Spain's baby boom was relatively small, although the population did not begin to decrease again until the late 1970s. Spain had one of the lowest fertility rates in the world at the end of the 1900s, and at the beginning of the twenty-first century, the fertility rate was at it's lowest point ever, reaching just 1.2 children per woman in 2000. This number has increased slightly in the past two decades, and is expected to be just over 1.3 in 2020.

The fertility rate of a country is the average number of children that women from that country would have throughout their reproductive years. In France in 1800, the average woman of childbearing age would have 4.4 children over the course of their lifetime. The beginning of the nineteenth century was a tumultuous time in France's history, involving France's revolutionary period, as well as the Napoleonic Empire. In the first decade of the 1800s, the fertility rate dropped by 0.4, before dropping more slowly, by another 0.5 between 1810 and 1850. The fertility growth rate fluctuated slightly in the late 1800s, before dropping drastically in the early twentieth century, falling from an average of 3 children per woman to less than 1.7 in 1920. France's fertility rate reached this point as a result of the First World War, and the influenza epidemic (known as the Spanish Flu) that followed. The interwar period saw a slight increase in fertility rate, before it fell again in the Second World War. Similarly to other major European countries after the war, France experienced a baby boom in the two decades following the war, before dropping again into the 1980s. The fertility rate reached it's lowest point in the post-war period, falling to 1.7 in 1995, before increasing in more recent years.

A chart indicating the likelihood of conception linearly declining with age (86% for women aged 20–24, 78% for 25–29, 63% for 30–34, 52% for 35–39, 36% for 40–44, 5% for 45–49, and 0% for 50 and over) is widely used on Internet fertility sites and by medical professionals. Its origin has been unknown until now. Through a literature survey, the author found that two books had contributed to the making of the chart. Among the seven points on the curve, three are based on data that are not the likelihood of conception, while four are probably derived from oversimplified description of fecundability estimates for American Hutterite and Taiwanese women in the 1950s and 1960s. At least two professionals are responsible for the fabrication or falsification of data.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In 1930, China's fertility rate was 5.5 children per woman, and this number then dropped to just under five over the next fifteen years, as China experienced a civil war and the Second World War. The fertility rate rose rather quickly after this to over 6.1 in 1955, before dropping again in the late 1950s, as Chairman Mao's 'Great Leap Forward' failed to industrialize the nation, and resulted in widespread famine that killed an estimated 45 million people. In the decade following this, China's fertility rate reached it's highest level in 1970, before the implementation of the two-child policy in the 1970s, and the one-child policy** in the 1980s, which radically changed the population structure. The fertility rate fell to an all time low in the early 2000s, where it was just 1.6 children per woman. However this number has increased to 1.7 today, and the two-child policy was reintroduced in 2016, replacing the one-child policy that had been effective for over 36 years.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In Germany in 1800, the average woman of childbearing age would have 5.4 children over the course of their lifetime. It remained around this number until the late 1820s, when it then dropped to just under five, which was a long-term effect of the Napoleonic Period in Europe. From this point until the end of the nineteenth century, Germany's fertility rate was rather sporadic, reaching it's lowest point in 1855 with an average of 4.6 births per woman, and it's highest point in 1875 (just after the foundation of the German Empire in 1871), with an average of 5.4 live births per woman. From the beginning of the twentieth century until the end of the Second World War, Germany's fertility rate dropped from around 5 children per woman in 1900, to 1.9 in 1945. The only time where the fertility rate increased was in the inter-war years. Like other countries heavily involved in the Second World War, Germany (both East and West) experienced a Baby Boom from the late 1940s to the late 1960s, however it then dropped to it's lowest point of just 1.3 children per woman by 1995, shortly after the re-unification of Germany. In recent years, Germany's fertility rate has gradually been increasing again, and is expected to reach 1.6 in 2020, its highest rate in over forty years.

In 1890, the total fertility rate in Ecuador was seven children per woman. This means that the average woman born in Ecuador in this time could be expected to have seven children over the course of her reproductive years. This fertility rate would gradually fall as Ecuador entered the 20th century, rising briefly in the 1920s during a period of economic and political instability. However, from the 1930s onwards, the fertility rate in Ecuador would begin falling, as medical advancements and increased access to healthcare saw child mortality rates fall; the fertility rate did plateau, however, during the global baby boom of the 1950s and 1960s, although the decline did resume in the 1960s. By the end of the century, fertility was at just 3.3 children per woman, and in the past two decades, it has fallen further, to 2.4 children per woman; which is above replacement level..

In China, the crude birth rate in 1930 was just under 39 live births per thousand people, meaning that 3.9 percent of the population had been born in that year. The crude birth rate dropped gradually over the next fifteen years, however it then rose to it's highest recorded figure by 1955. Between 1945 and 1950, the Second World War ended and the Chinese Civil War was finally coming to an end, and during this time the crude birth rate rose to almost 47 births per thousand in individual years. The crude birth rate dropped again in the late 1950s, as Chairman Mao's 'Great Leap Forward' failed to industrialize the nation, and resulted in a famine which killed an estimated 45 million people. The 1960s saw some recovery, where the figures rose from 36.4 to 39.5 births per thousand in this decade, however two-child and one-child policies were introduced in the 1970s and 80s, in an attempt to slow China's rapidly growing population. These measures led to the decline of the birth rate, dropping below fifteen births per thousand at the turn of the millennium. From 2000 until now the decline of China's crude birth rate has slowed, falling by just 2.8 births per thousand over the past twenty years, and it is expected to be just below twelve in 2020.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In 1800, Australian women of childbearing age would go on to have approximately 6.5 children on average over the course of their lifetime, and this number decreased gradually to just below five in the early 1850s. Over the next ten years the fertility rate increased to 5.7 children per woman, as an influx of migrants arrived on the continent during the Australian gold rushes, however the fertility rate dropped from 1860 until 1935, when it was then just 2.2 children per woman, although there was a small baby boom after the First World War. Australia's fertility rate did rise during the global 'Baby Boom' after the Second World War, reaching 3.4 in the 1960s, but it then dropped to two children per woman in 1980, and it has plateaued just under this number until today.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. In 1860, Canadian women of childbearing age would go on to have 5.7 children on average, however this number dropped significantly by 1925, where it was just 3.3. It then plateaued in the late 1920s, before dropping again, to 2.7 in 1940. Similarly to the United States, Canada experienced a large baby boom after the Second World War, rising to 3.9 in 1960, before declining again into the 1980s, and then plateauing between 1.5 and 1.7 until today. Canada's fertility rate is expected to be 1.5 children per woman in 2020.

In 1900, the crude birth rate of Turkey was approximately 48 births for every 1,000 people, meaning that just under 4.8% of the population was born in that year. This figure would closely follow the trends in fertility rate in Turkey, gradually falling for much of the first half of the 20th century. As women began having more children in the rapidly developing post-war economy of the 1950s. The crude birth rate also rose during this time, peaking at 49.3 children per thousand people in 1955. However, as Turkey would begin to modernize, the crude birth rate fell, as increased access to education and access to contraception among women would lead to a decline in the number of children the average woman would have. This decline has continued into the 21st century, and in 2020, it is estimated that just over 16 children were born for every thousand people in Turkey, accounting for 1.6% of the population.

In Canada, the crude birth rate in 1860 was forty live births per thousand people, meaning that four percent of the population had been born in that year. From this point until the turn of the century, the crude birth rate decreases gradually, to just over thirty births per thousand. Over the next twenty years, this number hovers just below thirty, and thereafter it decreases much more rapidly than before, to 20.7 in 1940, before Canada's baby boom in the 1940s, 50s and 60s, where the birth rate increased to over 27. From the end of the baby boom until the late 1970s the population decreases rapidly again, before the rate of decline then slows. Since 1975, the crude birth rate of Canada will have dropped from 15.6, to it's lowest point in 2020, where it is expected to be just 10.5 births per thousand people.

In 1875, Brazil's crude birth rate was 43.4 births per thousand people, which meant that 4.3 percent of the population had been born in that year. It is estimated that the figures remained around this level until the middle of the twentieth century, ranging from 41.7 to 46.9 births per thousand people between 1875 and 1945. Brazil's birth rate was going into decline in the 1940s, however the global baby boom which followed the Second World War then brought the birth rate back up to 44 in the 1950s. From this point until today, Brazil's birth rate has fallen rapidly, and in 2020 it is just 14 births per thousand; less than a third of what it was sixty years ago. The decline in Brazil's infant and child mortality rates were the driving factors behind this trend, along with quality of life improvements, such as improvements in medicine, education, access to contraceptives, among other things.

In 2024, the total population of Taiwan increased to approximately 23.4 million people. The significant drop in 2021 and 2022 was mainly due to people leaving the island during the coronavirus pandemic, while the natural growth rate was also slightly negative. The return of many people in 2023 led to a growth in population. According to national statistics and projections, population numbers entered a general declining path in 2020. Taiwan's demographic development Taiwan experienced rapid population growth in the 1950s and 60s, but alongside with economic development, growth rates decreased significantly. Falling birth figures have also been attributed to Taiwan’s family planning policy, which was aimed at keeping population growth at check. This led to a situation on the island where overall population density was very high and still growing, while the total fertility rate dropped quickly and eventually reached extremely low levels compared internationally. In the 21st century, the challenges of a quickly aging society became more and more apparent and the government initiated family friendly and birth promoting policies. However, fertility still kept on decreasing and reached a historical low in 2010 at 0.9 births per woman on average, and only in recent years has the number of births increased slightly. Implications of an aging society Today's Taiwan, like many East Asian societies, faces the challenges of a rapidly aging population. While the share of the population aged 65 and older accounted to around 18 percent in 2023, it is projected to reach 43 percent in 2060. The old-age dependency ratio, which denotes the relation of people of 65 years and above to the working-age population, is expected to reach around 87 percent in those years. This puts heavy pressure on the working people and the economy as a whole. However, compared to mainland China, which is in a very much comparable demographic situation, Taiwan enjoys the advantage of a relatively wealthy society, which helps to curb the negative economic effects of an aging population.