Sex ratios at birth in the British Isles over the past sixty years

The male-female ratio at birth (M/F: male births divided by total births) is anticipated to approximate 0.515. This has been shown to be declining in industrialised countries and to be displaying a latitude gradient in Europe, with more males born in warmer, southern climates. Annual national data for the British Isles for male and female live births were obtained from the World Health Organization and analysed with contingency tables. Analysis was performed separately for individual countries and for totals for the northern (Scotland and Northern Ireland) and southern (England and Wales, and the Republic of Ireland) regions. This study analysed 49,263,493 live births. There was an overall rise in M/F up to the late 1970s, followed by a decline thereafter. The step-down for the periods of 1975-1979 to 1980-1984 was highly significant for both the northern (p = 0.001) and southern regions (p < 0.0001). An overall decreasing trend in M/F was noted (p = 0.04) which reversed the expected European latitude gradient. More males are born in Scotland and Northern Ireland than in England and Wales, and the Republic of Ireland (p = 0.02). There was a male deficit of 59,311 live births.

M/F is decreasing in the British Isles, to the south more than to the north, to the extent that the expected latitude gradient is reversed. The interplay of several poorly understood factors is likely.