In 2000–2001, we measured DDT-related compounds in serum samples that had been collected during 1959–1967. The mean age of subjects when blood was drawn was 26 years. Samples collected within 1–3 days of delivery were used for 82% of the cases and 86% of controls, and serum drawn during the third trimester was used for the remainder. Longnecker et al. (1999) (link), reported that organochlorine levels assayed across all trimesters of pregnancy and soon after delivery were highly correlated, indicating that the time when samples are collected over the 9 months of pregnancy is not critical. We stored serum samples at −20°C. Samples were first thawed to prepare an aliquot of 1.5 mL for organochlorine assays. The aliquots were shipped frozen to the laboratory; p,p′-DDE, o,p′-DDT, and p,p′-DDT were assayed using methods reported previously by Gammon et al. (2002) (link). Sample order was randomly assigned within and across batches. Case–control pairs were analyzed in the same batches to minimize differences due to laboratory drift. The laboratory was blind as to case or control status of the samples. As described previously by Berkowitz et al. (2003) (link), we used all observed positive values of o,p′-DDT in analyses, even those reported to be below the limit of detection (LOD); seven o,p′-DDT measurements with reported negative values were recoded as the lowest measured value (i.e., 0.01 μg/L). Interbatch and intrabatch coefficients of variation were 16% and 5%, respectively, for p,p′-DDT; 11% and 4% for p,p′-DDE; and 26% and 5% for o,p′-DDT. Total cholesterol and total triglycerides were measured enzymatically on a Hitachi 911 analyzer (Roche Diagnostics, Indianapolis, IN) in a laboratory certified by the Centers for Disease Control and Prevention (Atlanta, GA) and the National Heart Lung and Blood Institute Lipid Standardization Program (Bethesda, MD).
Free full text: Click here
