The Fit for Delivery study: rationale for the recommendations and test-retest reliability of a dietary score measuring adherence to 10 specific recommendations for prevention of excessive weight gain during pregnancy.

Aiming at preventing excessive weight gain during pregnancy, 10 specific dietary recommendations are given to pregnant women in the intervention arm of the Norwegian Fit for Delivery (FFD) study. This paper presents the rationale and test-retest reliability of the food frequency questionnaire (FFQ) and a dietary score measuring adherence to the recommendations. The study is part of the ongoing FFD study, a randomised, controlled, intervention study in nulliparous pregnant women. A 43-item FFQ was developed for the FFD study. A dietary score was constructed from 10 subscales corresponding to the 10 dietary recommendations. Adding the subscales yielded a score from 0 to 10 with increasing score indicating healthier dietary behaviour. The score was divided into tertiles, grouping participants into low, medium and high adherence to the dietary recommendations. Pregnant women attending ultrasound screening at about week 19 of pregnancy were asked to complete the FFQ twice, 2 weeks apart. Of 154 pregnant women completing the first questionnaire, 106 (69%) completed the form on both occasions and was included in the study. The test-retest correlations of the score and subscales were r = 0.68 and r = 0.56-0.84, respectively (both P ≤ 0.001). There was 68% test-retest correct classification of the score and 70-87% of the subscales. In conclusion, acceptable test-retest reliability of the FFQ and the dietary score was found. The score will be used in the FFD study to measure adherence to the dietary recommendations throughout pregnancy and in the following year post-partum.