Relative validity of a semi-quantitative, web-based FFQ used in the ‘Snart Forældre’ cohort – a Danish study of diet and fertility

Abstract

Objective: To assess the relative validity of a semi-quantitative, web-based FFQ completed by female pregnancy planners in the Danish 'Snart Foraeldre' study. Design: We validated a web-based FFQ based on the FFQ used in the Danish National Birth Cohort against a 4 d food diary (FD) and assessed the relative validity of intakes of foods and nutrients. We compared means and medians of intakes, and calculated Pearson correlation coefficients and de-attenuated coefficients to assess agreement between the two methods. We also calculated the proportion correctly classified based on the same or adjacent quintile of intake and the proportion of grossly misclassified (extreme quintiles). Setting: Participants (n 128) in the 'Snart Foraeldre' study who had completed the web-based FFQ were invited to participate in the validation study. Subjects: Participants in the 'Snart Foraeldre' study, in total ninety-seven women aged 20-42 years. Results: Reported intakes of dairy products, vegetables and potatoes were higher in the FFQ compared with the FD, whereas reported intakes of fruit, meat, sugar and beverages were lower in the FFQ than in the FD. Overall the de-attenuated correlation coefficients were acceptable, ranging from 0·33 for energy to 0·93 for vitamin D. The majority of the women were classified in the same or adjacent quintile and few women were misclassified (extreme quintiles). Conclusion: The web-based FFQ performs well for ranking women of reproductive age according to high or low intake of foods and nutrients and, thus, provides a solid basis for investigating associations between diet and fertility.

Dietary Fat Intake and Fecundability in 2 Preconception Cohort Studies

“…Enrollment and primary data collection were conducted via online self-administered questionnaires. Beginning in January 2013 (10 days after enrollment), participants were invited to complete a comprehensive food frequency questionnaire (FFQ) designed specifically for this population (17). Eligible women were 18-45 years of age, residents of Denmark, in a stable relationship with a male partner, planning a pregnancy, and not receiving fertility treatment.…”

Dairy intake and fecundability in 2 preconception cohort studies

“…Although there were reasonable correlations between the FFQ and dietary recalls in each of the validation studies (18,20), some misclassification is inevitable. Because diet was assessed prospectively before the occurrence of infertility, any misclassification in our study is likely to be nondifferential, which would attenuate associations in the extreme categories of dairy intake toward the null.…”

“…Low-fat dairy intake was calculated by summing all servings of skim, 0.5%, 1%, and 2% milk, reduced-fat chocolate milk, low-fat yogurt, cottage and ricotta cheese, low-fat cheese, low-fat ice cream, frozen yogurt and sherbet, and low-fat dairy products in mixed recipes. In the Snart Foraeldre dietary validation study, deattenuated correlation coefficients comparing the FFQ to 4-d food records were 0.49 for high-fat dairy intake and 0.66 for low-fat dairy intake (18). In the DHQ validation study, deattenuated correlation coefficients comparing the FFQ to repeated 24-h dietary recalls were 0.78 for total dairy intake, 0.84 for milk, and 0.62 for cheese (20).…”

“…Enrollment and primary data collection were conducted via online self-administered questionnaires. Beginning in January 2013, 10 d after enrollment, participants were invited to complete a comprehensive food-frequency questionnaire (FFQ) designed specifically for this population (18).…”

“…Total dairy intake was estimated with the use of the nutrient composition of all food items on the FFQ and validated in each population (18,20). Total dairy intake was calculated by summing all servings of dairy from individual foods and mixed recipes.…”