The impact of maternal microbial transfer on the infant gut microbiome after cesarean delivery: a systematic review

OBJECTIVE: To systematically review the results of maternal microbial transfer in shaping microbial diversity, improving neonatal development, and evaluating the microbial transfer procedure's adverse events. DATA SOURCES: A comprehensive search was conducted on April 25, 2024, using PubMed/MEDLINE, Academic Search Ultimate, and ClinicalTrials.gov for studies published in English from 2000 to 2023. The following keywords were used: "vaginal seeding," "microbiota," "maternal fecal microbiota transplantation," "maternal microbial transfer," and "bacterial baptism." STUDY ELIGIBILITY CRITERIA: The review included English-language, peer-reviewed randomized controlled trials and nonrandomized interventional studies investigating maternal microbial transfer in neonates born via elective cesarean delivery. STUDY APPRAISAL AND SYNTHESIS METHODS: Data were extracted and analyzed for key outcomes, including severe adverse effects, alpha diversity, beta diversity, and the abundance of key taxa such as Bacteroides spp., Bifidobacterium spp., and Lactobacillus spp. RESULTS: A total of 10 studies, including 4 randomized controlled trials and 6 nonrandomized interventional studies with 1450 participants, were included in this qualitative review. The findings regarding changes in alpha diversity (a measure of microbial richness within individual samples) were inconclusive, while several studies indicated a potential increase in beta diversity (reflecting differences in microbial composition between samples) associated with the procedure. Bacteroides spp., Bifidobacterium spp., and Lactobacillus spp. were the most frequently assessed taxa, with some studies suggesting beneficial changes in their abundance. Developmental outcomes, such as anthropometric measures and allergy risks, showed limited evidence of benefit, with one study reporting preliminary findings of improved neurodevelopmental scores. No significant increase in severe adverse effects was observed in any of the included studies. CONCLUSION: The efficacy of maternal microbial transfer in restoring neonatal microbiota and promoting health outcomes remains uncertain, with neonatal outcomes addressed in only 3 of the included studies-one on allergy and one on neurodevelopment. However, while no serious adverse effects have been consistently reported, data on safety remain limited.