Relative Validity of a Food Frequency Questionnaire For Pregnant Women

Purpose: Pregnant women's diets should be monitored to ensure adequacy, but few studies have assessed the validity of dietary assessment tools among pregnant women. We examined the relative validity of a self-administered, semiquantitative food frequency questionnaire (FFQ) adapted for use in the International Trial of Antioxidants in the Prevention of Preeclampsia for assessing usual diet during pregnancy. Methods: A subsample (n=107) was recruited for the FFQ validation study, and provided three days of nonconsecutive three-day food records (3D-FRs) following completion of the FFQ. Results: Mean +/- standard deviation (median) energy intakes (kcal/kJ) from the FFQ and mean of 3D-FRs were 1963 +/- 610 (1860)/8219 +/- 2554 (7787) and 2320 +/- 607 (2354)/9713 2541 (9856), respectively. Spearman correlation coefficients between unadjusted FFQ and 3D-FRs nutrients were positive (r(S) ranged from 0.17 for iron to 0.49 for folate) and were generally statistically significant (0.05 <0.01). Most energy-adjusted correlations were less robust. Cross-classification of energy and 24 nutrients from the FFQ and means of the 3D-FRs placed 35% of them into identical quartiles and 75% into identical and contiguous quartiles; only 6% were frankly misclassified. Bland-Altman plots showed acceptable agreement between the two instruments. Conclusions: These results suggest that the FFQ is a relatively valid instrument for determining usual diet in pregnant women.