Validity and reproducibility of folate and vitamin B12 intakes estimated from a self-administered diet history questionnaire in Japanese pregnant women

Background: No validated dietary questionnaire for assessing folate and vitamin B-12 intakes during pregnancy is available in Japan. We evaluated the validity and reproducibility of intakes of folate and vitamin B-12 estimated from a self-administered diet history questionnaire (DHQ) in Japanese pregnant women. Methods: A sample of 167 healthy subjects with singleton pregnancies in the second trimester was recruited at a private obstetric hospital in metropolitan Tokyo from June to October 2008 (n = 76), and at a university hospital in Tokyo from June 2010 to June 2011 (n = 91). The dietary intakes of folate and vitamin B-12 were assessed using the DHQ. The serum concentrations of folate and vitamin B-12 were measured as reference values in the validation study. To assess the reproducibility of the results, 58 pregnant women completed the DHQ twice within 4-5 week interval. Results: Significantly positive correlations were found between energy-adjusted intakes and serum concentrations of folate and vitamin B-12 (r = 0.286, p < 0.001 and r = 0.222, p = 0.004, respectively). After excluding the participants with nausea (n = 121), the correlation coefficient for vitamin B-12 increased to 0.313 (p = 0.001). When participants were classified into quintiles based on intakes and serum concentrations of folate and vitamin B-12, approximately 60% were classified in the same or adjacent quintile. The intraclass correlation coefficients of the two-time DHQ were 0.725 for folate and 0.512 for vitamin B-12. Conclusion: The present study indicated that the DHQ had acceptable validity and reproducibility for assessing folate and vitamin B-12 intakes in Japanese pregnant women.