Validity of a questionnaire to estimate vitamin A intake in pregnant women

Abstract

The objective was to assess the relative validity of a food frequency questionnaire (FFQ) to estimate daily vitamin A intake in pregnant women using two biomarkers as references, maternal serum retinol and breast milk retinol. This is an observational, descriptive, analytical, cross-sectional study. FFQ was applied to 161 pregnant women at the largest public maternity hospital in Ribeirão Preto, Brazil. The FFQ recall period was the last 30 days before childbirth. The mother was asked if she had consumed or not each food item over the last 30 days, how often and which portion size. Samples of maternal blood and breast milk for determination of retinol concentrations were collected. Partial Pearson correlation test, agreement by kappa quadratic statistics, cross-classification into quartiles and the method of triads with two biomarkers were performed. The mean FFQ intake of vitamin A was 875 µg/day and the frequency of inadequate intake was 52.8%. Low correlation coefficients were observed between the FFQ and both biomarkers. In cross-classification, considering foods sources with or without provitamin A, 63.6% to 68.3% of the results fell into the same or adjacent quartiles, respectively; less than 10% of all results were classified into opposite quartiles. The validity coefficient of the FFQ was 0.484. FFQ performed better when considering only food sources of preformed vitamin A and both biomarkers (ρ=0.554). As a conclusion, FFQ provided an estimate of vitamin A intake with moderate accuracy, being suitable to rank pregnant women according to categories of intake.