There is increasing recognition that the microbiome may be important in the development of allergic disease. Asthma is the most prevalent pediatric chronic disease and affects more than 300 million people worldwide. For unclear reasons, those infants born at 34 weeks and earlier are three times as likely to develop asthma. Factors such as formula feeding, C-section delivery and antibiotic exposure may play a role. Recent evidence has identified a "critical window" in early life where gut and breast milk microbial changes are most influential. The investigators propose a novel study to follow a cohort of premature babies in the NICU and after discharge home. The investigators aim to examine whether various exposures of babies in the NICU impact their milk and gut microbiome and lead to asthma and allergies.

Our specific aims are:

1. To assess if there is a specific pattern of gut and/or breast milk microbiome over time that is affected by the type of nutrition a baby receives (donor vs maternal vs formula) or other exposures such as antibiotics.
2. Assess whether there are patterns in the microbiome associated with the development of allergic sensitization patterns.
3. Determine if early patterns of the microbiome and allergic sensitization predict allergic conditions (food allergies, allergic rhinitis, eczema, asthma) by 2 years of age.

The investigators will recruit approximately 50 subjects born at 34 weeks of gestation or earlier from two local level III NICU. These subjects will be followed over their NICU course with weekly stool, milk feed, and oral saliva collection as well as documentation of relevant events including prenatal history, delivery history, nutrition and breast feeding history and antibiotic courses. Further samples will be collected after discharge at research visits that will take place Rady Children's Hospital until 4-6 years of age. At these visits, standardized allergy questionnaires and a blood allergy panel will be obtained. Together this data will provide a unique opportunity to identify potential shifts in the microbiome associated with nutrition, asthma and allergy in preterm infants. Ultimately, the investigators may be able to discover ways to prevent the development of asthma and allergies during this early window of opportunity.

Inclusion Criteria:

• premature infant equal or less than 34 weeks of age

Exclusion Criteria:

• hypoxic ischemic encephalopathy, congenital anomaly that affects gastrointestinal system, unable to follow up

Premature infants born at equal or less than 34 weeks gestational age.

de-identified microbiome and metabolome data will be available.