2,3,7,8-Tetrachlorodibenzo-para-dioxin (TCDD), a, ubiquitous environmental contaminant, is associated with increased fetal loss and reduced birth weight in animal studies. In 1976, an explosion at a trichlorophenol plant near Seveso, Italy, resulted in the highest TCDD exposure known in human residential populations. In 1996, we initiated the Seveso Women's Health Study, a retrospective cohort study of women who resided in the most contaminated areas, Zones A and B. We examined the relation of pregnancy outcome in 510 women (Total pregnancies = 888) to maternal TCDD levels measured in serum collected shortly after the explosion. Ninety-seven pregnancies (10.9%) ended as spontaneous abortions (SAB). There was no association of log 10 TCDD with SAB (adjusted OR = 0.8, 95% CI = 0.6, 1.2); with birthweight (adjusted beta = -4 grams, 95% CI = -68, 60); or with small for gestational age births (SGA)(adjusted OR = 1.2, 95% CI = 0.8, 1.8). However, associations with birthweight (adjusted beta = -92 grams, 95% CI = -204, 19) and with SGA (adjusted OR = 1.4, 95% CI = 0.6, 2.9) were stronger for pregnancies within the first eight years after exposure. TCDD was associated with a 1.0 to 1.3 day non-significant adjusted decrease in gestational age and a 20% to 50% non-significant increase in the odds of pre-term delivery. It remains possible that the effects of TCDD on birth outcomes are yet to be observed, because the most heavily exposed women in Seveso were the youngest and the least likely to have had a pregnancy.
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