Reproducibility of reported nutrient intake and supplement use during a past pregnancy: a report from the Children's Oncology Group.

Maternal diet and nutrition have been thought to play a role in many childhood conditions. Studies using food frequency questionnaires (FFQ) have reported associations with maternal diet, but these findings are difficult to interpret because the reliability and validity of the FFQs for diet during a past pregnancy are not known. We determined the reproducibility of reported diet and supplement use during a past pregnancy in a subset of mothers interviewed for a case-control study of maternal diet in relation to the risk of childhood brain tumours. Cases were Children's Oncology Group patients, diagnosed at age <6 with medulloblastoma or primitive neuroectodermal tumour from 1991 to 1997. Area code, race/ethnicity, and birth date matched controls were selected by random-digit-dialling. Case and control mothers completed a modified Willett FFQ a mean of 5 years after the index child's birth. A mean of 3.6 months later, a subset of mothers consisting of 52 case and 51 control mothers repeated the interview; these comprise the reproducibility study population. The mean intra-class correlation was 0.59 (range 0.41, 0.69) for energy-adjusted nutrients from dietary sources only; it was 0.41 (range 0.06, 0.70) when supplements were included. Agreement for reporting multivitamin use during pregnancy by time period and pattern was good to very good (kappa = 0.66-0.85). Overall, the reproducibility of nutrient estimates and supplement use in pregnancy was good and similar to that reported for adult diet.