An Analysis of Seasonal Variation and Climatic Influences on the Male to Female Ratio of Live Births in Malta

Aims: In humans, male births occur in excess of female births. The ratio of male births to total births (MFR) is expected to approximate 0.515. Many factors have been shown to influence MRF and a seasonal pattern has also been described. This study was carried out in order to ascertain whether seasonal variation in MRF exists in Maltese live births and whether environmental influences exert any role.
Methods: Monthly live births subdivided by gender, were obtained from official Maltese government publications for the period 1958-2013. Analysis was carried out with SPSS, the Bio-Med-Stat Excel add-in for contingency tables and Demetra, using chi square tests, ANOVA, Freidman and Kruskall-Wallis tests, correlation, regression, and ARIMA models. Mean annual temperatures were available to 1958. Monthly data for maximum and minimum monthly temperatures, relative mean humidity, lowest relative humidity, hours of bright sunshine and rainfall was only available for 2001 to 2012.
Results: This study analysed 297254 live births (153652 males and 143602 females, MRF 0.5169, 95% CI 0.5151-0.5187). MRF exhibited a non-significant bimodal pattern (June and December peak). MRF displayed a significant negative correlation between MRF and average mean yearly temperature (p=0.049). There was an association between monthly mean relative humidity and MRF (p = 0.03).
Discussion: The nonsignificant seasonal pattern seen accords with that previously documented for other countries but the negative MRF correlation with mean annual temperature goes contrary to that previously documented in other countries. The humidity association has not been previously described.
Conclusion: Some seasonal variation may exist in MFR in Malta.