Declining male births with increasing geographical latitude in Europe.

OBJECTIVE Demographic studies in various industrialised countries have shown a decline in male births in the latter half of the 20th century from the expected ratio of 0.515 (males/total). This study analyses trends in this ratio over the period 1890 to 1995 in Malta, and also analyses this ratio for Western European countries for the period 1990-1995. DESIGN Births subdivided by sex were obtained from official Maltese publications. European countries were grouped according to geographical latitude by banding countries into three groups: Northern Mediterranean, Central European and Scandinavian. Births by sex for these countries were also analysed for the period 1990-1995. RESULTS No decline in the ratio of male births to total births was noted in Malta over the period 1916-1995. However, the ratio was higher than expected (n = 151,766, ratio = 0.517 (95% confidence intervals (95% CI): 0.514, 0.519). Moreover, during the period 1890-1899 (n = 66,874), the ratio was 0.523 (95% CI: 0.519, 0.527), even higher than observed during the 20th century (chi 2 = 8.3, p = 0.004). Analysis of European births showed a much higher ratio of male births in the south of Europe than in the north (chi 2 = 87.2, p < 0.0001). CONCLUSIONS The findings were unable to explain the higher incidence of male births in the south of Europe, but it is speculated that ambient temperatures may not only affect fertility, but also influence sex ratios at birth.