When very premature babies stay in the hospital after birth, their gut bacteria—the tiny living organisms in their stomachs—change in important ways. Researchers studied 58 extremely tiny babies (weighing less than 1,500 grams at birth) and 34 less premature babies over their first two months of life. They found that the tiniest babies had different types of bacteria in their guts compared to bigger premature babies. Things like whether babies were born naturally or by cesarean section, whether they received probiotics (helpful bacteria supplements), and complications during pregnancy all affected which bacteria grew in their stomachs. Understanding these differences could help doctors better protect premature babies from infections and help them grow healthier.

The Quick Take

  • What they studied: How the bacteria living in very premature babies’ stomachs change during their first two months in the hospital and what factors affect these bacteria.
  • Who participated: 92 premature babies total: 58 extremely tiny babies (weighing less than 1,500 grams, about 3.3 pounds) and 34 less premature babies (weighing more than 1,500 grams). Researchers collected poop samples from these babies during their hospital stay.
  • Key finding: Extremely premature babies had very different gut bacteria compared to less premature babies. The tiniest babies had more of certain bacteria types and showed signs of more active digestion. Things like how the baby was born (natural birth vs. cesarean section), whether they received probiotic supplements, and pregnancy complications significantly changed which bacteria grew in their guts.
  • What it means for you: If you have a very premature baby in the hospital, understanding their gut bacteria may help doctors make better decisions about feeding, probiotics, and infection prevention. However, this research is still early-stage, and parents should discuss findings with their baby’s medical team rather than making changes on their own.

The Research Details

Researchers collected poop samples from 92 premature babies during their first two months in the hospital. They used a special genetic test called 16S rRNA sequencing to identify and count all the different types of bacteria in each sample. This test is like taking a detailed census of the bacterial population—it tells scientists exactly which bacteria are present and how many of each type there are.

The study compared two groups: extremely tiny babies (under 1,500 grams) and less premature babies (over 1,500 grams). The researchers looked at how the bacteria changed over time and examined whether factors like delivery method (natural birth or cesarean section), probiotic use, and pregnancy complications affected the bacterial populations.

This type of study is called a prospective study, meaning researchers followed the babies forward in time and collected samples as events happened, rather than looking back at past records. This approach helps capture real changes as they occur.

The bacteria in a baby’s gut are incredibly important for health. They help fight infections, train the immune system, help digest food, and influence long-term health. Very premature babies have immature immune systems and are at high risk for serious infections, so understanding how their gut bacteria develop could lead to better ways to protect them. By identifying which factors change the bacterial populations, doctors might be able to make targeted decisions about probiotics, feeding methods, and other treatments.

This study has several strengths: it used advanced genetic sequencing technology to accurately identify bacteria, it followed babies over time rather than just taking one snapshot, and it examined multiple factors that might influence bacteria. However, the study size is relatively small (92 babies), and it was conducted in one hospital setting, so results may not apply to all premature babies everywhere. The study is descriptive, meaning it shows what happens but doesn’t prove that one factor directly causes changes in bacteria.

What the Results Show

The extremely premature babies (under 1,500 grams) had very different gut bacteria compared to less premature babies. The most common bacteria in the tiniest babies were Proteobacteria (about 66%) and Firmicutes (about 30%), which together made up 95% of all bacteria. The tiniest babies had significantly more Bacteroidetes bacteria compared to the less premature group.

The researchers also found that the tiniest babies showed signs of more active intestinal metabolism, meaning their digestive systems were working harder to process food and break down nutrients. This suggests their guts were developing and functioning differently than the less premature babies.

When researchers looked at specific factors, they found that three things significantly changed which bacteria grew: whether the baby received probiotics (helpful bacteria supplements), how the baby was born (natural delivery versus cesarean section), and whether there were complications with the placenta during pregnancy. Each of these factors influenced different types of bacteria, particularly Streptococcus, Clostridium, and Pseudomonas bacteria.

The study identified a total of 45 different bacterial groups (phyla) and 1,327 different bacterial types (genera) in the extremely premature babies. This shows incredible diversity in the bacterial populations. The research also confirmed that the gut microbiota is highly variable during the first two months of life, meaning the bacterial populations change significantly during this critical period. The findings suggest that hospital practices and medical decisions during this time window can meaningfully influence which bacteria establish themselves in premature babies’ guts.

Previous research has shown that premature babies have different gut bacteria than full-term babies, but this study provides more detailed information about extremely premature babies specifically. The finding that delivery method, probiotics, and pregnancy complications affect bacterial populations aligns with earlier research suggesting that these factors shape early bacterial colonization. However, this study provides more precise genetic identification of which specific bacteria are affected by these factors.

The study only included 92 babies from what appears to be a single hospital, so results may not apply to all premature babies in different hospitals or countries. The study describes what bacteria are present but doesn’t prove that changes in bacteria directly cause health problems or improvements. The researchers didn’t measure long-term health outcomes, so we don’t know if the bacterial differences they found actually affect whether babies get infections or develop other complications. Additionally, the study doesn’t explain why these factors change the bacteria—it just shows that they do.

The Bottom Line

Based on this research, there are no specific new recommendations for parents or doctors yet. The findings suggest that doctors should continue monitoring how probiotics, delivery methods, and pregnancy complications affect premature babies’ gut health, but more research is needed before making major changes to hospital practices. Parents of extremely premature babies should discuss gut health and probiotic use with their baby’s medical team, as individual circumstances vary. Confidence level: Low to Moderate—this is early research that needs confirmation.

This research is most relevant to parents of extremely premature babies (under 1,500 grams), neonatal intensive care unit (NICU) doctors and nurses, and pediatric researchers. Parents of less premature babies or full-term babies should not assume these findings apply to their situations. Healthcare providers in hospitals with different practices or populations may see different results.

Changes in gut bacteria happen continuously during the first two months of a premature baby’s life. If interventions like probiotics are used, effects on bacterial populations may appear within days to weeks, but effects on actual health outcomes (like infection rates) would take longer to measure—likely weeks to months.

Want to Apply This Research?

  • If your app serves NICU families, track: (1) Probiotic administration dates and types, (2) Feeding method changes (breast milk, formula, combination), (3) Delivery method and any pregnancy complications, and (4) Any infections or health changes. This allows families and doctors to see patterns between these factors and baby’s health over time.
  • Parents can work with their NICU team to document and discuss: which probiotics (if any) their baby receives, how feeding is progressing, and any changes in digestion or health. Using the app to record these details helps parents have informed conversations with doctors about their baby’s individual gut health needs.
  • Create a long-term tracking dashboard that shows: (1) Timeline of interventions (probiotics, feeding changes), (2) Baby’s health markers (infections, feeding tolerance, growth), and (3) Digestive symptoms (stooling patterns, feeding tolerance). This helps families and doctors identify patterns and make informed decisions about care as the baby develops.

This research describes how gut bacteria develop in extremely premature babies but does not provide medical advice. Parents of premature babies should not make any changes to their baby’s care, feeding, or probiotic use based on this study alone. All decisions about premature baby care should be made in consultation with the baby’s NICU medical team, who understand the individual baby’s specific health needs and circumstances. This study is early-stage research and has not yet been confirmed by larger studies or translated into clinical practice changes.