A Randomized Controlled Trial Investigating if Antibiotic Use in the First 48 Hours of Life Adversely Impacts the Preterm Infant Microbiome

Inclusion Criteria for antibiotic randomization: 1. Infant must be born between the gestational ages of 28 0/7 weeks and 34 6/7 weeks -AND- 2. Infant must be born at investigator's home institution. -AND- 3. Infant must be considered to have a low risk of infection by one of the following criteria: 1. Delivered for maternal indications (Cesarean section or induction of labor for maternal health, including pre-eclampsia, placental abruption, history of intrauterine fetal demise (IUFD)/abruption, multiple gestation requiring preterm delivery, etc) -OR- 2. Delivered due to preterm labor to a mother without the diagnosis of chorioamnionitis/maternal fever or prolonged rupture of membranes \>18 hours Exclusion Criteria for antibiotic randomization: 1. Signs of clinical illness within the first 3 hours of life: 1. 5-minute Apgar \<5 2. Requiring vasoactive drugs 3. Seizures 4. Significant respiratory distress requiring supplemental oxygen \>40% 2. Immature:Total (I:T) Ratio of \>0.2 on initial complete blood count (CBC) 3. Congenital anomalies, including renal anomalies requiring serum antibiotic level monitoring ANY infant born between the gestational ages of 28 0/7 weeks and 34 6/7 weeks who do not meet inclusion criteria, with parental consent, can participate in the stool analysis only arm of the study.