The sex ratio at birth in South Africa may be a sentinel health indicator

Introduction The sex ratio at birth is commonly expressed as M/T, denoting male births divided by total births. Males are almost invariably born slightly in excess. Stress and negative socioeconomic conditions lower M/T and this has been mooted as a possible reason for the observed low M/T for Black births worldwide. South Africa is experiencing a period of economic prosperity. This study was carried out in order to ascertain whether improving conditions in South Africa as measured by available health indicators, were associated with a rise in M/T in this country. Methods Annual male and female births were obtained from Statistics South Africa along with key health indicators: total fertility rate, life expectancy, infant mortality and under 5 year mortality, for 2003–2014. Results There were a total of 12,409,437 births (M/T 0.5035, 95% CI 0.5032-0.5037). There was a rise in M/T over the initial period studied (2003 − 2010) with a plateau thereafter. The rise over the entire period studied was significant (Chi for linear trend = 30.3, p < 0.0001). M/T was significantly positively correlated with life expectancy and significantly negatively correlated with infant mortality, under 5 year mortality and total fertility rate. Discussion It has been mooted that the lower M/T observed in Blacks may be stress-related. The observed rise in M/T associated with health improvements in South Africa support this contention. Moreover, this study suggests that M/T may serve as a sentinel health indicator, and may not only highlight adverse conditions through its decline, but also improvements in overall conditions with its rise.