The sex ratio at birth in South Africa increased 9 months after the 2010 FIFA World Cup

Abstract

Introduction: In humans in the absence of significant stress the sex ratio at birth [males/(males + females)] is in favor of more male than female live births.

Methods: This study sought to determine the influence of the 2010 Fédération Internationale de Football Association (FIFA) World Cup in South Africa on the sex ratio at birth in that country specifically 9 months afterwards. Publicly available data from Statistics South Africa was utilized detailing recorded live births. Analysis was carried out by Chi-squared tests.

Results: February and March 2011 about 9 months after the World Cup, had the highest observed sex ratio at birth (relatively more male births) of 0.5063 for the period 2003 to 2012. The observed sex ratio at birth in the considered two months of 2011 was 0.63% (p = 0.02) greater than the sex ratio at birth for corresponding periods from 2008 to 2012. The increase noted in 2011 corresponds to more than 1000 extra male births than expected for February and March 2011.

Conclusion: The 2010 FIFA World Cup was followed about 9 months afterwards by a significant increase in the sex ratio at birth. The main mechanism driving the observed increase in the sex ratio at birth in South Africa is most likely more frequent sexual intercourse at population level during the tournament.