TABLE 1

Infant Feeding Exposure Variables in the CHILD Birth Cohort

Exposure VariableDefinition and Categories
BF exclusivity at 3 mo • No BF (formula only)
 • Partial BF (breast milk supplemented with formula)
 • Exclusive BF after hospital (received some formula in hospital but only breast milk after discharge)
 • Exclusive BFa (breast milk only, both in hospital and after discharge)
BF mode at 3 mo • No BF (formula only)
 • Partial BF with formula (direct or expressed breast milk and formula)
 • BF only, some expressed (has received some breast milk expressed with a pump but no formula)
 • BF only, all directa (no expressed milk or formula since hospital discharge)
BF exclusivity at 6 moCategorized in 6 groups according to BF status and type of complementary feeding; collapsed into 4 groups for regression modeling
 • No BF: formula only, or formula plus solid food
 • Partial BF with formula: breast milk plus formula, or breast milk plus formula plus solid food
 • Partial BF without formula: breast milk plus solid food
 • Exclusive BFa: breast milk only, with no formula or solid food
Introduction of solid foodsAge of infant at first introduction of solid (or semisolid) foods, in mo
Evaluated as a continuous variable (for covariate adjustment) or categorized in 4 groups for regression modeling: <4, 4 to <5, 5 to <6, ≥6a mo
Duration of any BFAge of infant at weaning, determined from the first reported date of breastfeeding cessation. For breastfed infants with no reported cessation date because of skipped questionnaires (N = 367), the minimum confirmed breastfeeding duration was used. Evaluated as a continuous variable (for covariate adjustment) or categorized in 5 groups for regression modeling: never breastfed, <3, 3 to <6, 6 to <12, ≥12a mo
Duration of exclusive BFAge of infant at first introduction to formula, nonhuman milk, juice, or solid foods, in mo. Water and vitamin supplements were not considered. Evaluated as a continuous variable or categorized in 5 groups: never, <2, 2 to <4, 4 to <6, ≥6 moa
  • BF, breastfeeding.

  • a Reference categories for regression modeling, selected according to WHO recommendations.14