2.2. Study Design
This study was a single-center, placebo-controlled, double-blinded randomized trial of probiotics in healthy full-term infants conducted in Matsumoto City Hospital. This study protocol was performed in compliance with the Helsinki Declaration of 1975 as revised in 2013 and the Ethical Guidelines for Medical and Health Research Involving Human Subjects proposed by the Ministry of Education, Culture, Sports, Science and Technology and the Ministry of Health, Labor and Welfare; it was reviewed and approved by the Research Ethics Committee of Matsumoto City Hospital (27 September 2019). This study was registered on the UMIN Clinical Trials Registry (UMIN000038351).Prior to the initiation of the study, the investigator recruited participants from mothers giving birth at Matsumoto City Hospital and explained the details of the study according to the informed consent form. After giving birth, mothers completed a written consent form as a surrogate, and the infants who met the eligibility criteria were stratified by randomization schemes based on delivery mode (vaginal delivery/cesarean section) or sex (male/female) and assigned to two groups. Stratified randomization was utilized because delivery mode and gender have been shown to be influencing factors on early intestinal gut microbiota [