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

摘要: OBJECTIVES: Latitude gradients have been found in the male-female ratio at birth (M/F: male divided by total births), which is anticipated to be 0.515. METHODS: Annual national and female live births country were obtained from World Health Organization (WHO) analysed with contingency tables. The continent was arbitrarily into two regions: a region 10o above Equator 20o below Equator, second area Equator. RESULTS: This study analyzed 147,773,689 births. An overall increasing trend M/F for >20o (p S) latitudes < 0.0001). There 3,765,648 excess of what anticipated. CONCLUSION: South America, unlike decline present Europe North America. also showed that latitude are similar those previously reported more males being born cooler latitudes, contrary trends Europe. interplay several poorly understood factors likely.