Sex specific influence on the relationship between maternal exposures to persistent chemicals and birth outcomes.

Prenatal exposure to persistent pollutants has been associated with adverse birth outcomes, although few studies have investigated the influence of the sex of the infant. Sex specific differences have been associated with neurobehavioural impacts from environmental exposures with limited and contrary findings in relation to persistent pollutants. This study investigated the relationships between maternal exposure to a range of metals, polychlorinated biphenyls and pesticides measured in biological samples and birth outcomes with a specific focus on the sex of the infant. Outcome measures used included birth weight, birth length and head circumference, proportion of optimal birth weight (POBW), proportion of optimal birth length, proportion of optimal head circumference (POHC) and ponderal index. In general maternal urinary and blood metals, plasma polychlorinated biphenyl and pesticide concentrations were low. In adjusted regression models, a ln-unit increase in plasma β-hexachlorocyclohexane concentrations was associated with decreased birth weight (-76g, 95% CI -149, -33), ponderal index (-0.048, 95% CI 0.102, 0.007) and proportion of optimal birth weight (-1.5%, 95% CI -3.6, 0.5) in the whole study population, with stronger associations observed for male infants. Maternal p,p'-dichlorodiphenyldichloroethylene concentrations were associated with reduced ponderal index in male infants (β=-0.171, 95% CI -0.269, -0.074). A ln-unit increase in plasma hexachlorobenzene concentrations was associated with a 5% increase in POBW in male infants (95% CI 0.67, 9.5). Increased urinary barium was associated with increased birth length and POBL and decreased ponderal index in boys. Conversely, urinary concentrations of caesium and rubidium were found to be associated with decreased foetal growth in female infants. This study supports the growing body of evidence regarding the reductions in foetal growth associated with β-hexachlorocyclohexane and p,p'-Dichlorodiphenyldichloroethylene as well as reporting new relationships between metals exposures and birth outcomes. The finding that maternal exposure to barium, strontium, rubidium and caesium was associated with birth outcomes requires confirmation in larger studies. Similarly the apparent differences in susceptibility based on sex of the infant requires further investigation.