Authors
Davis, D.L., Gottlieb,M.B., Stampnitzky,J.R. (1998)

Reduced ratio of male to female births in several industrial countries: A sentinel health indicator?

This paper presents the hypothesis that the decline in the ratio of live born male to female infants over the last few decades, recently observed in several western countries (Canada, U.S., Netherlands and Denmark), should be examined as a sentinel indicator of an adverse impact of some environmental insult on human reproductive health. This ratio (Sex Ratio at birth - SRB) in typically around 1.06 (51.3%) and is apparently influenced by various factors. In this study, the authors reviewed historic trends in annual SRB data that had been published in papers that observed SRB decline, from the US (1970-1990), from Canada (1970-1990), the Netherlands (1950-1994), and Denmark (1960-1995). Regression of these data sets demonstrated a significant reduction in the annual SRB in the US of 0.1% over the 20-year period. This was slightly less than the declines reported from other nations (0.3% in the Netherlands, 0.22 % Canada and 0.2% Denmark). This 0.1% reduction in SRB corresponds to 38 000 fewer male infants than expected had no decline occurred. It should be noted that in none of these papers was there any attempt to correlate this change in SRB to specific exposures, occupations, demographic changes, etc., that may have influenced this outcome. Although the Davis et al. review did not identify specific exposures of the entire population that could cause such an effect, studies linking exposures to pesticides, studies that had correlated exposure to dibromochloropropane, dioxin, pollution from iron foundries, etc. to reduced SRB were cited. The authors speculate that these historic trends in reduced population SRB could be a consequence of widespread exposure to some pollutants that are causing decreased reproductive health and specified concerns about exposures to endocrine disrupting substances as being culpable. Other factors that have been shown to influence SRB were also discussed including stress, parental age gap, and extent of prenatal care, medical conditions and therapeutic drug use. Moreover, it should be noted that there is very little data in the literature concerning the mechanisms whereby the sex ratio can be altered. The strength of the Davis et al. review lies not in what it demonstrates but rather the hypothesis that it proposes and can be tested in animal experiments.