This cross-disciplinary study will assemble and longitudinally follow a large, diverse birth cohort to determine the relationships between early life antibiotic exposure, microbiome development, growth, antibodies, and immunostimulation.

Perinatal and infant antibiotic exposures are common and have been linked to changes in the gut microbiome, which plays a central role in health and disease. Childhood obesity is an epidemic and animal models have linked antibiotic induced changes in the microbiome with increased adiposity. Infants become colonized with trillions of bacteria in the first few hours of life. During this time period, their nascent immune system develops tolerance to commensal microbes

The primary objectives are to measure the impact of common perinatal and early childhood antibiotic exposures on the structure and function of the developing gut microbiome. To determine the association between common perinatal and early childhood antibiotic exposures and weight/adiposity gain in a large birth cohort of children. To determine mechanisms for the association between microbiome changes over time and the rate of weight/adiposity gain in a large birth cohort of children. To determine the normal developmental pattern by which healthy children develop antibodies in their blood against the microbes that naturally colonize their intestines. To determine the association between immunostimulation and protection from persistent colonization in humans.

Inclusion Criteria (if not specified, applies to child):

• Born at Pennsylvania Hospital
• Recruited at <120 hours of age
• Born at ≥36 0/7 weeks gestation
• Birth weight ≥2000 grams
• Parents plan to receive well-child care in the Children's Hospital of Philadelphia (CHOP) network, Society Hill Pediatrics, Center City Pediatrics, Penn Medicine or South Philly Pediatrics
• Biological mother is the legal guardian, or the child is born from a surrogacy with guardianship immediately transferred in hospital

Exclusion Criteria (if not specified, applies to child):

• Child in neonatal intensive care unit (NICU) for >120 cumulative hours
• Biological mother NOT legal guardian, except surrogacy where guardianship is transferred at birth
• Biological mother NOT primary caretaker, except surrogacy where guardianship is transferred at birth
• Biological mother < 18 years of age
• Child has culture confirmed (blood or cerebrospinal fluid cultures) infection
• Biological mother is non-English speaking

Our study population will be comprised of children born at Pennsylvania Hospital between 2016-2018 and subsequently, followed in the Children's Hospital of Philadelphia (CHOP) Care Network or one of four other local primary care pediatric practices.

De-identified individual participant data will be shared with collaborators at the Knights Lab at the University of Minnesota.