Observable variations in human sex ratio at birth

Yanan Long, Qi Chen, Henrik Larsson, Andrey Rzhetsky

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


The human sex ratio at birth (SRB), defined as the ratio between the number of newborn boys to the total number of newborns, is typically slightly greater than 1/2 (more boys than girls) and tends to vary across different geographical regions and time periods. In this large-scale study, we sought to validate previously-reported associations and test new hypotheses using statistical analysis of two very large datasets incorporating electronic medical records (EMRs). One of the datasets represents over half (∼ 150 million) of the US population for over 8 years (IBM Watson Health MarketScan insurance claims) while another covers the entire Swedish population (∼ 9 million) for over 30 years (the Swedish National Patient Register). After testing more than 100 hypotheses, we showed that neither dataset supported models in which the SRB changed seasonally or in response to variations in ambient temperature. However, increased levels of a diverse array of air and water pollutants, were associated with lower SRBs, including increased levels of industrial and agricultural activity, which served as proxies for water pollution. Moreover, some exogenous factors generally considered to be environmental toxins turned out to induce higher SRBs. Finally, we identified new factors with signals for either higher or lower SRBs. In all cases, the effect sizes were modest but highly statistically significant owing to the large sizes of the two datasets. We suggest that while it was unlikely that the associations have arisen from sex-specific selection mechanisms, they are still useful for the purpose of public health surveillance if they can be corroborated by empirical evidences.
Original languageEnglish (US)
Pages (from-to)e1009586
JournalPLOS Computational Biology
Issue number12
StatePublished - Dec 2 2021
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2022-01-27
Acknowledged KAUST grant number(s): FCS/1/4102- 02-01, FCC/1/1976-26-01, REI/1/0018-01-01
Acknowledgements: We are grateful to E. Gannon and M. Rzhetsky for comments on earlier versions of this manuscript.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

ASJC Scopus subject areas

  • Ecology
  • Cellular and Molecular Neuroscience
  • Ecology, Evolution, Behavior and Systematics
  • Genetics
  • Modeling and Simulation
  • Computational Theory and Mathematics
  • Molecular Biology


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