Published online by Cambridge University Press: 06 January 2012
This investigation aims to contribute to the existing literature on demographic and ecological factors affecting the sex ratio at birth, by analysing the births in Croatia from 1998 to 2008. Data from birth certificates for all Croatian births for the investigated period (n=420,256) were used to establish the link between parental ages, birth order, region of birth, parental occupation and parental education level, and sex of the child. The χ2 test and t-test were used to assess the significance of each of the factors, along with multiple logistic regression to control for possible confounding effects. The results suggest that a joint higher age of both parents significantly lowers the sex ratio at birth. There is also a regional variation in sex ratio at birth, the lowest value being in Central Croatia and the highest in the City of Zagreb. Changes in the reproductive physiology of older parents are most probably responsible for the lower sex ratio, although the limited sample size warns against widespread generalizations. The causes of the regional variation in sex ratio at birth are most likely the different regional levels of obesity and physical inactivity.