RESEARCH REPORT

Secular trends in sex ratios at birth in North America and Europe over the second half of the 20th century

V Grech¹, P Vassallo-Agius², C Savona-Ventura³

¹ Paediatric Department, St Luke’s Hospital, Malta
² Medical School, University of Malta
³ Department of Obstetrics and Gynaecology, St Luke’s Hospital, Malta

Correspondence to:
Correspondence to:
Dr V Grech, Paediatric Department, St Luke’s Hospital, Guardamangia, Malta;
victor.e.grech{at}govt.mt

Context: A previous study showed that significantly more boys were born in southern latitudes in Europe than in northern latitudes and the converse pattern was observed in North America.

Objective: This study analyses secular trends in gender ratios for live births over the second half of the 20th century.

Design, setting, participants: Analysis was carried out from a World Health Organisation dataset comprising live births over the above period. This included 127 034 732 North American and 157 947 117 European live births.

Main outcome measures: Analysis of trends in gender ratios for countries in both continents.

Results: The findings show a highly significant overall decline in male births in both Europe and North America (p<0.0001), particularly in Mexico (p<0.0001). Interestingly, in Europe, male births declined in North European countries (latitude>40°, p<0.0001) while rising in Mediterranean countries (latitude 35–40°, p<0.0001). These trends produced an overall European male live birth deficit 238 693 and a North American deficit of 954 714 (total male live birth deficit 1 193 407).

Conclusions: No reasonable explanation/s for the observed trends have been identified and the causes for these trends may well be multifactorial.

Keywords: sex ratio; birth rate; climate

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