The foetal and neonatal periods are the developmental periods of extraordinary plasticity (adaptation) and much of the structural and physiological development at this time is now known to remain with us into adulthood.
By 12 months of age, the composition of the infant’s microbiome starts to resemble that of an adult gut and we are no longer able to permanently influence the structure and diversity of this bacterial community.
Key factors that have been shown to impact gut microbiome development during this period are mode of delivery, feeding type, hospitalisation, gestational age (pre-term) and antibiotic administration.
Colonisation at birth
First colonisation of the gastro-intestinal tract (GIT) by the microbiota occurs at birth. Although there is some evidence to show that there are low numbers of foetal and placental microbiota, this is currently considered to be part of the preparation of the baby’s immune system for the outside world and the intestine of the healthy newborn infant can be considered to be sterile.
The microbial flora is acquired immediately following birth via contamination/inoculation from the environment the baby is born into. The newborn gut is a perfect microbial habitat as it contains food, moisture and warmth, which enable the microbes to colonise and start to grow.
For vaginal birth, the first colonisation is from the vaginal, skin and rectal microflora of the mother – 90% of the microbiota present in the baby in the first few days of life have been shown to reflect the vaginal flora of the mum, being mainly lactobacillus species (primarily acidophilus strains).
For caesarean-section (C-section) birth, this first colonisation comes from skin and hospital environment flora.
As a result, the microbial population of the gastro-intestinal tract of babies born by vaginal birth differs significantly from that of babies born by C-section, as follows: