In a recent study published in The Lancet, researchers presented comprehensive estimates of past and future trends in fertility across 204 nations and territories from 1950 to 2100.
Study: Global fertility in 204 countries and territories, 1950–2021, with forecasts to 2100: a comprehensive demographic analysis for the Global Burden of Disease Study 2021. Image Credit: fizkes/Shutterstock.com
Background
Fertility assessments are critical for resolving geopolitical, environmental, economic, and social challenges caused by shifting population age trends and migration. They impact policies addressing resource and healthcare needs, education, labor supply, family planning, and gender equality.
The United Nations Population Division and the United States Census Bureau have been updating fertility rates since the 1950s. The Wittgenstein Centre for Demography and Global Human Capital worked with the Global Burden of Diseases, Injuries, and Risk Factors Study to develop current demographic projections for 2100.
About the study
In the present study, researchers explored global fertility trends across 204 nations and territories between 1950 and 2021, with forecasts to 2100.
To predict fertility indicators between 1950 and 2021, the researchers analyzed GBD 2021 data using spatiotemporal Gaussian regressions and linear mixed-effects regressions with fixed effects variables (female educational attainment and contraception met need).
They used data from 8,709 nation-years of sample and vital registrations, census, 1,455 surveys, and 150 additional sources to calculate age-specific fertility rates (ASFR) for five-year age intervals between 10 and 54 years. They added ASFRs across ages to calculate the total fertility rate (TFR).
The researchers determined live births by multiplying the ASFRs by the age-specific feminine population and then adding them for ages between 10 and 54 years.
The Institute for Health Metrics and Evaluation (IHME) model evaluated the complete cohort fertility at the age of 50 years (CCF50), modeled using the meta-regression-Bayesian, regularized, trimmed (MR-BRT) approach.
GBD 2021 predicted fertility metrics for females in 204 nations and territories divided into 21 regions and seven super-regions. The methods used to predict fertility from 1950 to 2021 were similar to those used in GBD 2019.
The researchers anticipated fertility using CCF50 up to the 2085 female birth cohort, then predicted ASFR for each five-year age interval as a fraction of CCF50. The researchers used linear-type mixed-effects models, spline interpolation, and an autoregressive integrated moving average (ARIMA) model (1,0,0) on residuals to predict the age pattern of fertility for each cohort.
The researchers also forecasted multiple alternative situations in every location, including achieving the United Nations Sustainable Development Goals (SDG) for literacy by 2030, meeting the contraceptive needs SDG by 2030, enacting pro-natal government policies to develop supportive surroundings for individuals giving birth, and combining the prior three scenarios.
Results
Between 1950 and 2021, worldwide TFR fell by more than half, from 4.8 to 2.2. Global yearly live births peaked at 142.0 million in 2016, falling to 129.0 million by 2021.
The fertility rates have fallen in all nations compared to 1950, with the total fertility rates remaining over 2.10 canonically regarded fertility replacement levels among 94 (46.0%) by 2021. The findings comprised 44 out of 46 nations in the sub-Saharan regions of Africa, the areas with the highest proportion of live births (29% in 2021).
Forty-seven nations and territories whose lowest predicted fertility rates in the 1950-2021 period were below the replacement level saw at least one consecutive year of higher fertility; three places recovered above the replacement levels. Fertility rates in the future would fall worldwide, with global TFRs of 1.8 in 2050 to 1.6 in 2,100 in the reference situation.
According to the forecasts, the list of nations having fertility rates above replacement would drop from 24% (n=49) in 2050 to 2.90% (n=6) by 2100, three of which falling into the low-income category for the GBD sub-Saharan region of Africa, as determined by the World Bank in 2021.
In the forecasts, Sub-Saharan parts of Africa accounted for more than 50% of live births by 2100, up from 41% in 2050 to 54% in 2100. Most of the remaining super region share of live births would reduce from 2021 to 2100, with South Asia falling from 25% during 2021 to 17% by 2050 and further to 7.10% by 2100.
In contrast, the Middle East, Northern Africa, and the high-income-type super-areas would exhibit more live births. Forecast projections for alternate scenarios indicate that reaching SDG objectives for contraception and educational requirements and enacting pro-natal health policies would lead to worldwide total fertility rates of 1.70 and 1.60 by 2050 and 2100, respectively.
Prediction skill measure values for IHME forecasting models were positive for all ages, implying that it outperformed the constant estimation.
Conclusions
Global fertility rates are declining, with over half of all countries in 2021 recording rates below the replacement level. This trend, observed since 2000, reveals significant variations in the rate of decline, with only a few countries experiencing a minor rebound, yet none have returned to replacement levels.
Moreover, the geographic distribution of live births is shifting towards lower-income countries. Despite potential efforts through pro-natal policies, future fertility rates are expected to continue decreasing globally.
These demographic shifts will lead to profound economic and societal impacts, including ageing populations and shrinking workforces in wealthier nations, alongside a growing proportion of livebirths in the world's poorest areas.
Genetic insights into reproductive health and longevity