1000 days

The gut microbiota at birth and during early life plays a major role in the immune, metabolic, endocrine, and neural pathways. These pathways are highly interdependent and influenced by the environment, nutrition, and infections.

It is considered that from conception to two years of age is a critical window for early growth and development, referred to as ‘the first 1000 days’. Disruption to the infant microbiome may contribute to lifelong and intergenerational deficiencies in growth and development.

On becoming pregnant, the microbiota changes and continues to change throughout pregnancy. Vaginal infections, such as bacterial vaginosis and the translocation of maternal gut bacteria, influence the in-utero environment. Certain bacteria are thought to cause pre-term births and babies with low birth weight or small for gestational age (SGA). Prenatal microbiota may also influence immune development, impacting post-natal growth trajectories.

The maternal gut contributes to most bacterial species present in the microbiota of a healthy newborn. The mode of birth also shapes the microbiota. Disruption of maternal transmission by caesarean section and subsequent antibiotic exposure around birth is associated with a higher incidence of pathogen colonisation and immune-related disorders in children. Maternal transmission of gut bacteria via vaginal birth promotes healthy growth and disease resistance. Early feeding practices also contribute to the early microbiota, with an estimated 25-30% of the infant’s microbiota originating from breast milk.

Growing evidence has shown increased colonisation of gas-producing bacteria, such as Escherichia coli and Klebsiella, and lower colonisation of anti-inflammatory bacteria, Bifidobacterium and Lactobacillus in the first meconium is related to infantile colic.

From the introduction of solid foods at around six months, the diversity of the microbiota increases rapidly, and concurrently, this period represents a crucial period for child growth. The gut microbiota and immune system development are intimately linked in early life.

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