Calibration of a semi-quantitative food frequency questionnaire in early pregnancy

Purpose We assessed the validity of a semi-quantitative food frequency questionnaire (FFQ) among pregnant women. Methods We enrolled 72 African American and 132 Caucasian pregnant women in a calibration study of an existing FFQ. For eight categories of intake of fatty acids, carotenoids, and γ- tocopherol estimated by the FFQ (energy-adjusted deciles 1, 2, 3, 4+5, 6+7, 8, 9, 10) we compared measurements of the corresponding nutrient level measured in pooled blood specimens from all participants in each category. Results For α-carotene, plasma levels were 1.9 (p = 0.10) and 2.9 (p = 0.0007) μg/L higher for every 100 μg increase in dietary intake among African American and Caucasian women, respectively. A high percent increase in plasma levels was apparent between extreme dietary deciles of α-carotene (275% for African American and 152% for Caucasian women). Increases across deciles were evident for lycopene, lutein, and γ-tocopherol, ranging from 12% to 64%. We also observed relationships between dietary intake and their erythrocyte concentrations of long-chain n-3 fatty acids and trans-fatty acids, but not α-linolenic acid. Conclusion The observed differences in biomarkers across varying levels of dietary intake suggest that this FFQ is an appropriate epidemiologic tool for assessing intake of at least several important nutrients during early pregnancy in both African American and Caucasian women.