Acquisition of microbiota according to the type of birth: an integrative review.

Only two electronic databases were searched, and only papers in Portuguese, English or Spanish from a ten-year period were included, so some relevant studies may be missing. The review included non-randomized controlled trials, cohort studies and cross-sectional studies, so it shows associations rather than proof that birth route causes immune or health outcomes. Included studies examined different body sites and time points, and some reported no significant differences, so the pattern is not uniform. Other early-life factors, such as antibiotics, feeding and hospital environment, may also affect microbiota, so birth route cannot be separated from all of them. The authors stated that it is impossible to exhaust the entire literature on this topic.

Do not conclude that vaginal birth prevents asthma, immune disorders or obesity, or that C-section should be avoided when medically needed. This review mainly reports differences in newborn microbiota, and many included studies are observational, so it does not prove a causal clinical benefit.