Neonates delivered by scheduled Cesarean Section will be randomized to receive vaginal seeding (exposing the infant to Mother's vaginal flora) or sham. Infants will be followed for three years to examine health outcomes including microbiome development, immune development, metabolic outcomes, and any adverse events.

Cesarean section (CS) delivery is a common surgical procedure intended to increase the chances of successful delivery and to protect the health of the mother and baby. Yet this intervention is overused and has been associated with higher risk of immune and metabolic disorders in the offspring. It is hypothesized that these associations are due to CS-delivered newborns not receiving the full inoculum of maternal microbes at birth.

While restoring labor is not possible, restoring the microbes that colonize infants during birth through exposure to vaginal flora, is feasible, and has been shown in a small pilot study, to normalize the microbiota of the intestine, skin and mouth during the first month of life.

The investigators hypothesize that the restoration of the vaginal microbiota to the infant at birth will restore the infant microbiome and decrease the risk of obesity and other immune-mediated diseases linked with CS. The investigators aim to test this hypothesis in a randomized controlled trial by first examining the effect of vaginal seeding, in CS-delivered newborns, on the gut microbiota composition, structure and function (Phase I of study; first 50 infants) and then on the BMI z score and other immune-mediated outcomes (Phase II of study; 600 infants).

Methods: CS-delivered neonates will be randomized to either an experimental arm with exposure to the maternal vaginal microbiota at birth, or a control arm with no exposure. Feces, skin, saliva, breast milk, and vaginal swabs will be collected for microbiome analysis. The investigators will obtain clinical information from in-person visits, surveys and the electronic health record.

Implications: this randomized controlled clinical study will provide evidence of whether the "vaginal seeding" procedure can safely transfer microbes from mom-to-baby, and whether these microbes are beneficial for the metabolic and immune health of the child.

Inclusion Criteria for Mother:

• Scheduled for cesarean delivery at ≥ 37 weeks
• Pregnant with single fetus, in good general health, age 18 years or older
• Negative maternal testing for infections transmitted through vaginal and/or other body fluids performed as standard of care tests in early pregnancy
• Negative testing for Group B strep at 35-37 weeks gestation
• Vaginal pH ≤ 4.5 indicative of Lactobacillus-dominated vaginal microbiota
• No maternal or fetal complications that may inhibit the ability to perform microbiome restoration per protocol
• English or Spanish speaking
• Negative maternal testing for Gonorrhea, Chlamydia, Hepatitis B, Hepatitis C, Syphilis, and HIV at 35 weeks gestation or later
• Women aged 18-29 years must have a normal Pap test within 3 years
• Women aged 30-65 years must have a normal Pap test and an HPV test (co-testing) within 5 years or FDA-approved primary hrHPV testing alone within 5 years or a normal Pap test alone within 3 years
• Negative maternal testing for SARS-CoV-2 for the delivery admission performed as standard of care test at the Inova Health System.

Inclusion Criteria for Infant:

• Infant condition after delivery requires no more than standard neonatal resuscitation* or is otherwise medically unable to receive the full VMT procedure

[*] Standard neonatal resuscitation may include: tactile stimulation, bulb suction, oxygen without positive pressure, or drying

Exclusion Criteria for Mother:

• Delivery at a hospital other than Inova Health System
• Cesarean delivery scheduled for active infection that would have interfered with vaginal delivery such as genital herpetic lesions
• Rupture of membranes prior to scheduled cesarean delivery
• Bacterial vaginosis within 30 days of cesarean delivery
• Symptomatic urinary tract infection within 30 days of cesarean delivery
• Antibiotic therapy within 30 days of cesarean delivery (exclusive of medication use for prophylaxis at the time of surgery)
• Symptoms on admission suggesting Chorioamnionitis, e.g. maternal fever, fundal tenderness
• Symptoms on delivery admission of possible vaginal infection such as genital herpetic lesions
• History of genital HSV
• History positive testing for Group B strep infection
• History of a child with a diagnosis of Group B strep sepsis
• Pregnancy a result of donor egg or surrogacy
• Preexisting history of Type I or Type II Diabetes
• Maternal history of documented genital HPV infection, positive HPV testing or genital warts on physician examination
• Positive maternal testing for SARS-CoV-2 within 30 days of delivery or symptoms on admission suggesting potential Covid-19 infection

Individual participant data will be shared with co-principal investigators (Maria Gloria Dominguez-Bello at Rutgers University and Noel Mueller at Johns Hopkins School of Medicine).