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Association between prevalence of placental malaria and antibody levels. The malaria-specific antibody levels were categorized into four groups: negative (N); low positive (L); medium positive (M); and high positive (H). The positive cutoff was the mean + 3 standard deviations of the negative control samples. Further categorization of antibody-positive women is described in the Materials and Methods section. The P values were derived from the Cochran-Armitage trend test.
