Results of the analyses investigating the ability of a single sample to correctly identify a woman as highly exposed (based on her 3 month geometric mean metabolite level) are shown in Table 3. Sensitivity, specificity, positive predictive value, and negative predictive value were high for both metabolites (range 0.8 to 0.9), suggesting good agreement between methods of classifying women into the high exposure group (i.e. geometric mean throughout pregnancy or a single measurement). Results were similar when we used uncorrected concentrations (data not shown) and specific gravity corrected observations (Table 3).