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Observational Study
. 2025 Jul 1;15(1):21677.
doi: 10.1038/s41598-025-05445-8.

Effects of sport disciplines on offspring sex ratio in elite athletes: an observational study

François B Favier  1 , François D Desgorces  2   3 , Grégoire Bosselut  1 , Thierry Launay  4   5 , Grégoire P Millet  6 , Florian Alexis Britto  7   8
Affiliations
Observational Study

Effects of sport disciplines on offspring sex ratio in elite athletes: an observational study

François B Favier et al. Sci Rep. .

Abstract

The sex ratio (SR; the ratio of male to female births) is a demographic indicator close to 1.04 in the worldwide population that can variate depending in several environmental conditions. The practice of elite sport exposes athletes to several factors known to impact SR, in particular high physiological (training loads) and psychological (management of personal and professional life) levels of stress. However, knowledge about the effect of elite sport practice on SR is limited. We used binomial logistic regression to analyze the SR of the offspring (n = 2995 births) of 2132 athletes (18.7% of females) from various sports including 1597 athletes selected in their national team. We showed that endurance elite athletes are more likely to have daughters compared to athletes from mixed or power-oriented disciplines. Furthermore, classification tree analysis revealed that the probability of siring daughters was strongly enhanced in female athletes who gave birth during their professional sport career (SR = 0.581). Our results highlight the practice of elite sport as a condition associated with specific adaptation of the reproductive system. This raises questions about the mechanisms responsible for SR alteration (ranging from physiological to socio-economic aspects), opening new avenues in sports sciences and in reproductive biology.

Keywords: Elite sport; Gender inequality; Human reproduction; Sex-ratio.

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Conflict of interest statement

Declarations. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
SR in elite Athletes from different sport disciplines. (a) Most represented sport disciplines of the experimental sample ranked according to the SR of athletes. Disciplines with the same color belong to a same category on the (b); (b) SR of elite athletes categorized into four categories depending on the nature of the sport disciplines; (c) male vs. female comparison; and (d) active (during) vs. retired (after the sport career) comparison. n number of births analyzed. Dashed line represents mean SR worldwide (1.04).
Fig. 2
Fig. 2
Classification tree analysis for predictors of offspring sex from elite athletes. Parental age was added as influential variable into the model. The tested predictors were sport category (endurance, mixed, power or skill), sex of the athlete (female or male), period (active or retired) and sport level (international or national).
Fig. 3
Fig. 3
Hypothetical causal diagram of mechanisms that could alter sex ratio in elite athletes.
See this image and copyright information in PMC

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