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01 June 2023
Published online 12 August 2021
Prenatal discrimination will skew sex ratios worldwide.
Around five million fewer girls are expected to be born by 2030 – a figure that could soar to 22 million by the end of the century in a worst-case scenario.
The natural sex ratio at birth (SRB), defined as the male-to-female ratio of live births, falls within a range of 1.03 to 1.07 depending on ethnicity. However, access to foetus ultrasound scans has resulted in sex-selective abortions and skewed SRB in several countries. This is estimated to account for approximately 50 million fewer females born over the last 50 years.
An international research team led by King Abdullah University of Science and Technology (KAUST), Saudi Arabia, used a database of more than three billion birth records from 204 countries to estimate SRB imbalances at global, regional and national levels until the year 2100.
Under a conservative scenario, sex imbalances at birth are set to decline, but will still lead to millions of missing females before reaching natural SRB levels. The model predicts 4.7 million fewer girls by 2030, and an additional one million by the end of the century. This stems from the expected future trends of 12 countries with evidence of ongoing or past skewed SRB, including India and China, which have the highest numbers of annual births in the world.
The researchers modelled another possible future scenario where the SRB rises in 17 countries with son preference, including Egypt, Jordan and Morocco, which do not currently show a strong evidence of unbalanced SRB. In this hypothetical case, the world is set to ‘lose’ 5.9 million girls during the next decade and 16.2 million between 2031 and 2100, with sub-Saharan Africa accounting for about 40% of the missing births.
“We make our scenario-based projections available to policymakers in order to provide data-driven and model-based information on what the best-case and worst-case scenarios might be,” says statistician Fengqing Chao, from the Biostatistics Group at KAUST.
The researchers acknowledge the limitations of their models due to uncertainties associated with this type of long-term projection, and highlight the need to monitor and address the factors behind the persistence of gender bias to accelerate the return to natural SRB levels.
“The attempt of the authors to project SRB levels is noteworthy, especially because prior attempts relied on simpler and much more unreliable methods,” says sociologist, Dario Pavić from the University of Zagreb, Croatia, who was not involved in the study. “The diversity of the SRB trajectories for different countries should warn against ‘one-size-fits-all’ policy solutions that do not take into account the cultural, economic, demographic and social characteristics of different countries and regions.”
Chao, F. et al. Projecting sex imbalances at birth at global, regional and national levels from 2021 to 2100: Scenario-based Bayesian probabilistic projections of the sex ratio at birth and missing female births based on 3.26 billion birth records. BMJ Global Health 6, e005516 (2021).