Biological monitoring of environmental exposures in pregnant women: Stability of biomarkers and contribution of tobacco smoke exposures

Biological monitoring, estimating exposure to environmental chemicals through measurement of the chemical or its metabolites in biological tissues, has proved a reliable and useful tool for exposure assessment. Increased awareness of the special vulnerability of the pregnant woman and fetus to environmental exposures has prompted an expansion of studies in this population. However, little is known about the effect of pregnancy on the interpretation of biological monitoring values relative to non-pregnant women. Known physiological changes such as plasma volume expansion could affect the levels of contaminants found in the mother. The effect of pregnancy on levels of biological markers of 58 contaminants was assessed in 505 pregnant subjects drawn from a series of national surveys conducted by the CDC (Third National Report on Human Exposure) for the years 1999-2002. Levels of many contaminants appeared unaffected by trimester of pregnancy. Some metals and phthalate concentrations declined from first to third trimester, implying that exposures might be underestimated in pregnant women. Many organochlorine levels appeared to increase over the pregnancy, which may reflect increased mobilization from adipose tissue and present an exposure risk to the fetus. The metals antimony and cadmium and most polycyclic aromatic hydrocarbon metabolites were significantly correlated (p<0.01) with cotinine, implying that smoking or exposure to environmental tobacco smoke represents a major source of these contaminants for pregnant women. It is important for researchers to determine the magnitude of the effect pregnancy has upon the interpretation of biological markers in order to support studies in this vulnerable population.