Abstract
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 127034732 North American and 157947117 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 degrees, p<0.0001) while rising in Mediterranean countries (latitude congruent with 35-40 degrees, p<0.0001). These trends produced an overall European male live birth deficit 238693 and a North American deficit of 954714 (total male live birth deficit 1193407). CONCLUSIONS: No reasonable explanation/s for the observed trends have been identified and the causes for these trends may well be multifactorial.