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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 (rS ranged from 0.17 for iron to 0.49 for folate) and were generally statistically significant (0.05<p<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.