To validate the modified FFQ, estimated total iron intake during the third trimester was compared with biomarkers of iron status such as serum ferritin, soluble transferrin receptor (sTfR), and the sTfR:F index at delivery. Data were tested for normality using the D¡¯Agostino-Pearson test. Differences between groups were tested using t tests or Mann-Whitney tests. Correlations were tested using Spearman¡¯s ¦Ñ. Significance was set at P < 0.05.
Significant crude and energy-adjusted serum ferritin and total iron intake were related (¦Ñ?= 0.30; P < 0.05) in women without GDM. Serum ferritin, sTfR, and the sTfR:F index were different (P < 0.05) between women with intakes above and below the recommended levels. Cross-classification showed agreement between methods in mothers with and without GDM; on average, 63 % of the women were classified into the same or adjacent quartile when ranked by FFQ and iron status.
These findings suggest the Willett FFQ is a good tool for assessing total iron intake of French-Canadian pregnant women.