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See Pregnancy and Lactation tables
Identifying and studying additional biomarkers of energy and nutrient intake will advance validation efforts and lead to a better understanding of the biases and sources of measurement error in dietary assessment instruments in pregnant or lactating populations. Currently very limited information is available on systematic measurement error, including both group-specific bias and person-specific bias in these populations for the 24HR (24-Hour Recall), FR (Food Record) or FFQ (Food Frequency Questionnaire) instruments. Although difficult and expensive, large-scale studies of free-living pregnant women at various stages of pregnancy using biomarkers, such as the DLW (Doubly Labeled Water) method for measurement of TEE (Total Energy Expenditure), paired with the various dietary assessment instruments would be helpful. Similar studies with lactating women at various postpartum stages would be useful. Research is needed to identify other pregnancy or lactation-specific laboratory indices for nutritional evaluation. Research is also needed to identify sensitive, noninvasive, and specific biomarkers of functional reproductive outcomes (12). Yang and Erickson reviewed surveys of folic acid status in non-pregnant or lactating women of reproductive age and have examined the relationship of blood folate concentrations to reported supplement and food intake. They found significant reporting error in supplement use. Similar studies in pregnant or lactating women are needed (63).
Certainly the methods research priority recommendations from the "Future Directions for the Integrated CSFII-NHANES" 2002 workshop (9;64) can be applied to pregnant or lactating women. Among the recommendations are:
- Determine ways to identify and remove bias associated with under- and over-reporting of food, beverage, and supplement intake in 24HR interviews;
- Further develop and pilot test propensity questionnaires (frequency-type questionnaires) to augment information collected in 24HRs and estimate the proportion of users of infrequently consumed foods;
- Develop and validate improved methods for assessing dietary supplement use; and
- Determine the best way to assess severity of inadequacy and excess nutrient intake (9;64).
In a longitudinal survey, the optimal timing and frequency of dietary assessment in pregnant and lactating women should be examined. The impact of social desirability bias, body-mass index, and maternal weight gain on self-reports of food, beverage, and supplement intake at various stages of pregnancy and lactation have not been well studied. Further work is needed on the most appropriate instruments for low-literacy populations, various ethnic groups, and adolescent pregnancies. Validation of automated or web-based dietary assessment methods is needed.