The investigators will use existing data from two US longitudinal birth cohorts that tracked mother-child dyads from pregnancy to adolescence: 1) Project Viva (1999-present) that enrolled 2,341 pregnancies and followed 2,128 children at delivery, 6 months, then yearly from 1 year to 15 years of child age, and 2) the Infant Feeding Practices Study II (IFPS II, 2005-2007) that enrolled 3,033 pregnancies with surveys in late pregnancy, neonatal (1 month), then monthly from 2 months (N=2,552) to 12 months of infant age, and at 6 years. For Aim 1, the investigators will classify infants based on their age of egg introduction: never, \<2 months, 2-3 months, 4-5 months, 6-8 months, 9-11 months, and 12 months. The investigators will compare physical growth, obesity, cardio-metabolic health, food allergy, and cognition test scores in mid-childhood and adolescence. The investigators will fit multi-variable linear or logistic regression models with fractional polynomial functions of the infant age of egg introduction. Both linear (e.g., earlier introduction, a higher probability of the outcome) and non-linear (e.g., threshold effect) associations will be tested. For Aim 2, The investigators will classify infants based on their frequency of egg intake: never, \<once/week, once/week, 2-4 times/week, nearly daily or daily, and 2 times/day. The investigators will use similar analytic methods mentioned above to compare their later outcomes. Finally, the investigators will create an average probability of multiple child outcomes to balance across different aspects of child health and development. The investigators will identify the lowest-risk infant egg consumption when the corresponding average predicted probability of the related adverse outcomes is the lowest.
