Exposure Variable | Definition 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 BF^{a} (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 direct^{a} (no expressed milk or formula since hospital discharge) | |

BF exclusivity at 6 mo | Categorized 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 BF^{a}: breast milk only, with no formula or solid food | |

Introduction of solid foods | Age 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, ≥6^{a} mo | |

Duration of any BF | Age 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, ≥12^{a} mo |

Duration of exclusive BF | Age 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 mo^{a} |

BF, breastfeeding.

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

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