The first years of life represent a critical period in human development, and growing research suggests that the trillions of microorganisms living in the gut may play a far more important role in health than previously imagined. From pregnancy and birth through infancy and early childhood, the developing microbiome appears to influence everything from growth and immune function to brain development and disease risk. Recent studies have highlighted the potential benefits of probiotics—beneficial live microorganisms—in supporting both maternal and infant health.
One of the most significant areas of research concerns premature infants, who face unique health challenges due to their underdeveloped digestive and immune systems. Very preterm babies are at increased risk of developing necrotising enterocolitis (NEC), a severe intestinal disease that can be life-threatening. A large Swedish study conducted by researchers at the Karolinska Institutet analysed data from 4,695 babies born prematurely between 2017 and 2024. The researchers compared outcomes in 1,571 infants who received a daily probiotic supplement containing three carefully selected bacterial strains with 3,124 infants who did not receive probiotics.
The findings were striking. Infants who received probiotics experienced significantly lower rates of NEC and mortality during their stay in neonatal intensive care. The combined risk of NEC or death was 0.8% among babies receiving probiotics, compared with 3.4% among those who did not. Mortality alone was reduced from 1.4% to 0.3%, while NEC incidence fell from 2.5% to 0.6%. Statistical analyses suggested that a substantial portion of the reduced mortality could be explained by the lower incidence of NEC. Importantly, no increase in serious bloodstream infections (sepsis) was observed among infants receiving probiotics. While the study was observational and cannot definitively prove cause and effect, the results add to a growing body of evidence supporting probiotic use in very preterm infants born between 28 and 31 weeks of gestation.
The influence of beneficial bacteria may begin even before birth. Research from the University of Cambridge has demonstrated that the maternal gut microbiome can directly affect foetal development. In a mouse study, researchers investigated the effects of Bifidobacterium breve, a naturally occurring beneficial bacterium commonly found in the human gut and frequently used in probiotic supplements. Pregnant mice receiving Bifidobacterium breve showed improvements in placental function and nutrient transport to the developing foetus. Most notably, the offspring exhibited enhanced brain metabolism and developmental processes associated with healthy brain growth.
The findings suggest that maternal gut bacteria may play a previously underappreciated role in supporting foetal brain development. Researchers observed increased delivery of nutrients to the developing brain and favourable changes in cellular pathways linked to growth and neurological development. Although these findings were obtained in animals and require confirmation in human studies, they raise the possibility that targeted probiotic interventions during pregnancy could one day help support healthy foetal development, particularly in pregnancies affected by growth restriction.
The importance of beneficial bacteria does not end at birth. Research published in Nature involving more than 900 children and over 12,500 stool samples has provided valuable insights into how the infant microbiome develops during the first years of life. Scientists found that the bacterial community within the gut evolves through three distinct phases: a developmental phase during the first 14 months of life, a transitional phase from 15 to 30 months, and a stable phase beginning at around 31 months of age. By approximately two-and-a-half years of age, the microbiome begins to resemble the more stable bacterial ecosystem typically seen in adults.
A key finding was the central role of Bifidobacterium species during infancy. These beneficial bacteria were abundant in breastfed infants and closely associated with components naturally present in breast milk. However, once breastfeeding ceased and solid foods became a greater part of the diet, Bifidobacterium levels declined rapidly and were replaced by bacterial groups more characteristic of the adult microbiome. Researchers noted that this transition occurred more quickly than expected and appeared to be driven by the changing nutritional environment within the gut.
The study reinforces the well-established benefits of breastfeeding while also highlighting the importance of understanding how breast milk supports microbial development. Scientists believe that identifying the nutrients in breast milk that selectively promote beneficial bacteria such as Bifidobacterium may help develop nutritional strategies for infants who cannot be breastfed. Probiotic supplementation containing carefully selected strains of Bifidobacterium is one area of particular interest.
Researchers also observed that factors such as mode of delivery, exposure to siblings, household pets, and geographic location influenced microbiome development. Vaginal delivery, for example, was associated with temporary increases in certain beneficial bacterial populations. These findings emphasise that microbiome establishment is shaped by a combination of nutrition, environment and early-life experiences.
Beyond digestive health, the microbiome may have long-term implications for disease risk. Additional analyses from the TEDDY study found differences in the gut bacteria of children who later developed type 1 diabetes compared with those who did not. Infants who remained free of the disease possessed microbiomes richer in genes associated with fermentation and the production of short-chain fatty acids—compounds believed to support intestinal health and immune regulation.
Taken together, these studies paint a compelling picture of the microbiome as a crucial contributor to health from the earliest stages of life. Beneficial bacteria appear to influence outcomes before birth, support healthy development during infancy, and may even affect long-term disease risk. Probiotics, particularly strains belonging to the Bifidobacterium family, are emerging as promising tools for supporting gut health in both mothers and infants.
While further research is needed—especially large human clinical trials—the evidence increasingly suggests that nurturing a healthy microbiome may be one of the most important foundations for lifelong health. Whether through maternal gut health during pregnancy, breastfeeding, or carefully selected probiotic supplementation, supporting beneficial bacteria during these formative years may offer lasting benefits that extend well beyond the gut.