A new study published online on February 9, 2015 in the peer-reviewed journal Environmental Research, investigates the association between urinary concentrations of several non-persistent chemicals with the secondary sex ratio (SSR), defined as the ratio of male to female live births. Bae and colleagues focused on substances with endocrine-disrupting properties, namely, bisphenol A (BPA, CAS 80-05-7) and several phthalates. Their analysis includes 220 couples with a singleton birth from the U.S.-based Longitudinal Investigation of Fertility and the Environment (LIFE) study. The authors collected urine samples from the couples when they were attempting to conceive and analyzed them for BPA and 14 phthalate metabolites. The relative risks of a male birth in relation to the measured urinary concentrations of the substances were then estimated. The results suggests that paternal preconception exposure to BPA and mono-isobutyl phthalate (MiBP) may be associated with decreased SSR i.e., an excess of female births. Contrarily, maternal preconception exposure to BPA and mono-n-butyl phthalate, MiBP and mono-benzyl phthalate may increase the SSR. The authors stress that these associations were only observed when both partners’ concentrations were modeled jointly, highlighting the importance of assessing couples in relation to the SSR. Therefore, studies incorporating both partners’ hormonal profiles and other relevant reproductive outcomes are needed to eventually understand the effects of these chemicals on human sex selection, the authors conclude.

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Bae, J. et al. (2015). “Couples’ urinary bisphenol A and phthalate metabolite concentrations and the secondary sex ratio.Environmental Research 137, 450–457.