Researchers studied whether giving premature babies more breast milk early on would change their gut bacteria in helpful ways. They compared two groups of very premature infants—one receiving larger amounts of breast milk and one receiving smaller amounts—in the first 36 hours after birth. By two weeks old, the babies’ gut bacteria looked surprisingly similar between the two groups. This suggests that while breast milk is still important for premature babies, the amount given in those first few days might not dramatically change their gut bacteria diversity as quickly as scientists thought it might.

The Quick Take

  • What they studied: Whether giving premature babies larger amounts of breast milk right after birth would create more diverse and healthier gut bacteria compared to giving them smaller amounts
  • Who participated: 95 very premature babies (born around 31 weeks, weighing about 3.3 pounds on average) who were randomly assigned to receive either larger or smaller amounts of breast milk in their first 36 hours of life
  • Key finding: By day 14 after birth, babies who received more breast milk did not have noticeably different or more diverse gut bacteria compared to babies who received less breast milk
  • What it means for you: If you have a premature baby, this research suggests that while breast milk feeding is still very important, the amount given in the first day or two may not be the main factor determining gut bacteria diversity in the short term. Talk with your medical team about the best feeding plan for your baby’s specific situation.

The Research Details

This was a randomized controlled trial, which is one of the strongest types of medical research. Researchers randomly divided 95 very premature babies into two groups. One group received larger amounts of breast milk (60-80 milliliters per kilogram of body weight per day), while the other group received smaller amounts (20-30 milliliters per kilogram per day) during their first 36 hours after birth. The researchers collected stool samples from all babies around day 14 after birth and analyzed them to see what bacteria were present and how diverse the bacterial communities were. By randomly assigning babies to groups, the researchers could be more confident that any differences they found were due to the amount of breast milk, not other factors.

Understanding how to build healthy gut bacteria in premature babies is important because gut bacteria play a role in digestion, immune system development, and overall health. If researchers could show that giving more breast milk early on created better gut bacteria, it might lead to new feeding recommendations for premature babies. This study used a randomized design, which is important because it helps rule out other explanations for why babies’ gut bacteria might differ.

This study has several strengths: it used random assignment to reduce bias, it analyzed actual bacterial samples using modern genetic testing, and it included a reasonable number of babies. However, the study only looked at bacteria at one time point (day 14), so it doesn’t tell us what happens later. The sample size of 95 babies is moderate—larger studies might find effects that this one missed. The study was published in a peer-reviewed journal, meaning other experts reviewed the work before publication.

What the Results Show

The main finding was surprising: babies who received more breast milk in the first 36 hours did not have more diverse or richer gut bacteria by day 14 compared to babies who received less breast milk. Scientists measured diversity in two ways—richness (how many different types of bacteria) and Shannon diversity (a more complex measure of diversity)—and neither showed significant differences between the groups. The researchers also looked at the overall composition of bacteria communities and found no meaningful differences between the two groups. This suggests that the amount of breast milk given in the first day or two after birth may not be the main factor determining gut bacteria diversity in these very premature babies during the first two weeks of life.

The researchers identified four different patterns of bacterial communities that developed in the babies, but these patterns appeared in both groups equally. This means that while babies’ gut bacteria do develop in recognizable patterns, the amount of early breast milk feeding didn’t push babies toward one pattern or another. The findings suggest that other factors—such as the type of antibiotics given, the baby’s individual genetics, or other aspects of medical care—might be more important in shaping early gut bacteria.

Previous research had suggested that early breast milk feeding might help create more diverse and beneficial gut bacteria in premature babies. This study challenges that assumption, at least for the first two weeks of life. The results don’t mean breast milk isn’t important—it clearly is for premature babies—but they suggest that the timing and amount in the very first hours may not be the critical factor for gut bacteria diversity that researchers expected. This finding adds nuance to our understanding of how premature babies’ gut bacteria develop.

This study has several important limitations. First, it only looked at bacteria at one time point (day 14), so it doesn’t show what happens later as babies grow. Second, the study included 95 babies, which is a moderate sample size—a larger study might have found differences that this one missed. Third, the study didn’t follow babies long-term to see if differences in early feeding affected their health outcomes later. Fourth, the study only measured bacteria diversity, not whether the bacteria were actually beneficial or harmful. Finally, all babies were in a hospital setting receiving medical care, so results might not apply to all premature babies in all situations.

The Bottom Line

Based on this research, there is moderate evidence that the amount of breast milk given in the first 36 hours after birth may not be the main factor determining gut bacteria diversity in very premature babies during the first two weeks. However, breast milk remains very important for premature babies’ nutrition and health. Parents and medical teams should continue following current feeding guidelines for premature babies, which typically emphasize starting breast milk as soon as possible and increasing amounts gradually. Individual babies may have different needs, so work closely with your medical team to develop the best feeding plan.

This research is most relevant to parents of very premature babies (born before 32 weeks), neonatal intensive care unit (NICU) doctors and nurses, and pediatricians who care for premature babies. It may be less relevant to parents of babies born closer to full term. If your baby is premature, discuss these findings with your medical team in the context of your baby’s specific situation.

This study only measured bacteria at day 14, so it doesn’t tell us about longer-term effects. It may take weeks or months for differences in gut bacteria to develop and affect health outcomes. If you’re interested in your premature baby’s gut health, ask your medical team about monitoring over months, not just days.

Want to Apply This Research?

  • If tracking a premature baby’s feeding, record daily breast milk volume (in milliliters per kilogram of body weight), any formula or other nutrition given, and any digestive symptoms or feeding tolerance. This data can help parents and doctors see patterns over time.
  • Parents can use a feeding app to log each breast milk feeding session, including timing and amount, to ensure consistent feeding schedules and help medical teams optimize nutrition. This creates a clear record for discussions with the NICU team about feeding progression.
  • Track feeding amounts, growth measurements (weight gain), and digestive tolerance (stooling patterns, feeding intolerance signs) weekly. Share this information with your medical team to ensure your premature baby is progressing well. While this study suggests early breast milk amount may not dramatically change gut bacteria diversity quickly, consistent tracking helps identify what works best for your individual baby.

This research applies specifically to very premature babies (born around 31 weeks gestation) in hospital settings. The findings should not be interpreted as advice to reduce breast milk feeding for premature babies—breast milk remains critically important for premature infant nutrition and health. All feeding decisions for premature babies should be made in consultation with your neonatal care team, as individual babies have different medical needs. This study measured only gut bacteria diversity at one time point and did not assess long-term health outcomes. If you have a premature baby, discuss these findings with your doctor or NICU team to understand how they apply to your baby’s specific situation.