Validation of a food-frequency questionnaire for assessing vitamin intake of Japanese women in early and late pregnancy with and without nausea and vomiting.

Maternal vitamin intake during pregnancy is crucial for pregnancy outcomes and the child's subsequent health. However, there are few valid instruments for assessing vitamin intake that address the effects of nausea and vomiting during pregnancy (NVP). This study aimed to investigate the validity of a FFQ concerning vitamin intake during early and late pregnancy with and without NVP. The participants comprised 200 Japanese pregnant women who completed the FFQ and from whom blood samples were taken in early and late pregnancy. Energy-adjusted dietary vitamin intakes (vitamin C, folate, vitamin B6, vitamin B12, vitamin A, vitamin E and vitamin D) from FFQ were compared with their blood concentrations. A subgroup of women with NVP was investigated. In early pregnancy, significant correlations between FFQ and biomarkers were observed for vitamin C (r 0·27), folate (r 0·18) and vitamin D (r 0·26) in women with NVP and for vitamin A (r 0·18), vitamin B12 (r 0·24) and vitamin D (r 0·23) in women without NVP. No significant correlations were observed in either group for vitamins B6 or E. In late pregnancy, similar significant associations were observed for vitamin C (r 0·27), folate (r 0·22), vitamin B6 (r 0·18), vitamin B12 (r 0·27) and vitamin A (r 0·15); coefficients were higher among women without NVP. Our study demonstrates that the FFQ is a useful tool for assessing intake of several important vitamins in early and late pregnancy regardless of NVP status.