Table 1

Overview of primary (PO) and secondary (SO) outcomes and methods for the randomized controlled trial (RCT)

OutcomeVariableMeasureInstrumentSample size* (incl. dropout)†
Preconception diet (PO)‡Overall diet
Diet quality
Food and nutrient intake
Diet score
2×24 hour recall (myfood24)
Food propensity questionnaire
211 (264)§
Preconception Health-related quality of life (SO)Health-related Quality of lifeSelf-reported quality of lifeSatisfaction with life scale
RAND-12 Health Status Inventory
Pregnancy health (SO)Gestational weight gain (GWG)GWG (absolute measure and relative to guidelines)Data retrieved from MBRN as recorded in pregnancy records and birth certificate1100 (1375)¶
Hypertensive disordersPreeclampsia yes/no
Gestational diabetesGestational diabetes yes/no2517 (3147)**
Neonatal health (SO)Growth measures at birthBirth weight, length and head circumferenceData retrieved from MBRN.
LGA/SGA1044 (1305)**
Gestational age-adjusted weight/lengthBirth weight≥4000 g
Newborn adiposity
Preterm delivery
Ponderal index (kg/cm‡)<37 weeks of gestation461 (577)**
  • *Numbers needed in each group. Calculated with a statistical power of 80% and type 1 error of 5%.

  • †Accounted for a 25% dropout rate in line with other interventions.30

  • ‡Measured at baseline, post intervention and follow-up.

  • §Healthy Eating Index from The Norwegian Mother, Father and Child cohort (MoBa) (mean score 49.8±7.3 (SD)) used as a proxy for the planned PRECDIET score. As even small improvements in diet are relevant to public health, we assume an increase of 2 points to have a public health impact.

  • ¶Estimation based on the 1 kg decrease in GWG with SD from.28

  • **Based on proportions from Medical Birth Registry of Norway (MBRN), assuming improvement in line with previous group differences in pregnancy.30

  • LGA, large for gestational age; SGA, small for gestational age.