A study conducted by the U.S. National Institute for Occupational Safety and Health found no relationship between paternal occupational exposure to the dioxin TCDD and preterm birth. That study used a pharmacokinetic model to estimate worker’s serum TCDD concentration at the time of conception (Lawson et al., 2004). Similarly, a study of veterans of Operation Ranch Hand, who were responsible for spraying herbicides during the Vietnam War, failed to find consistent effects of paternal exposure to TCDD (which is present in Agent Orange) on the rates of preterm birth (Michalek et al., 1998). In the latter study, the paternal dioxin level measured in 1987 or 1992 was extrapolated to the time of conception of the child to estimate the level of TCDD exposure.
In summary, the few studies that have assessed paternal toxicant exposure failed to find evidence of an increased risk for preterm birth as a result of paternal occupational exposure to lead or TCDD.
As discussed more extensively elsewhere in this report, preterm births are more prevalent among African American women than among women of other racial-ethnic groups, and this pattern has persisted over the years. The terms “environmental justice” and “environmental racism” describe the disproportionate burden of environmental pollution on poor and minority populations (Brown, 1995; Silbergeld and Patrick, 2005). A recent review by Silbergeld and Patrick (2005) discusses in detail the disproportionate exposures of those populations to environmental pollutants and the effects on birth outcomes. Although the latter review emphasizes birth outcomes other than preterm birth, its discussion includes reports of racial-ethnic differences in environmental exposures that are relevant to preterm birth. Silbergeld and Patrick (2005) concluded that, “exposures to these toxicants may explain part of the socioeconomic disparity that is observed in terms of risks of adverse pregnancy outcomes” (Silbergeld and Patrick, 2005).
Despite the persistent racial-ethnic disparities in the rates of preterm birth and the increased awareness of racial-ethnic disparities in environmental exposures, few studies have considered the interactions among raceethnicity, environmental chemical exposures, and preterm birth. Woodruff et al. (2003) reported increased levels of air pollution in neighborhoods consisting predominantly of minority populations and, after adjusting for maternal risk factors that included race-ethnicity, found a small increase in the odds of preterm delivery (OR 1.05; 95% CI 0.99–1.12) in association with high levels of air pollution.
Other factors that may influence exposure in racially and ethnically distinct patterns include behavioral, cultural, and sociological characteristics and practices. In a case-control study (188 preterm births and 304 nor-