RESUMO
OBJECTIVES: South Korea has experienced unprecedented ups and downs in the sex ratio at birth (SRB), which has been a unique phenomenon in the last two decades. However, little is known about socioeconomic factors that influence the SRB. Employing the diffusion theory by Rogers, this study was undertaken to examine the trends in social variations in the SRB from 1981 to 2004 in Korea. METHODS: The data was taken from Vital Birth Statistics for the period from 1981-2004. We computed the annual male proportion of live births according to the parental education (university, middle/high school, primary) and occupation (non-manual, manual, others). Logistic regression analysis was employed to estimate the odds ratios of male birth according to social position for the equidistant three time periods (1981-1984, 1991-1994, and 2001-2004). RESULTS: An increased SRB was detected among parents with higher social position before the mid 1980s. Since then, however, a greater SRB was found for the less educated and manual jobholders. The inverse social gradient for the SRB was most prominent in early 1990s, but the gap has narrowed since the late 1990s. The mother's socioeconomic position could be a sensitive indicator of the social variations in the sex ratio at birth. CONCLUSIONS: Changes in the relationship of parental social position with the SRB were detected during the 1980-2004 in Korea. This Korean experience may well be explained by diffusion theory, suggesting there have been socioeconomic differences in the adoption and spread of sex-detection technology.