Good Bacteria for Tiny Tummies: What the Latest Research Says About Probiotics for Premature Babies

A plain-language guide to a 2025 study that combined 51 trials to ask which probiotics best protect premature infants from a dangerous bowel disease

A large 2025 study combined the results of 51 separate trials involving 11,661 premature babies to ask a practical question: do probiotics — the "good bacteria" sold for gut health — actually protect tiny infants from a serious bowel disease called necrotizing enterocolitis, and if so, which probiotic works best? The answer was encouraging but nuanced. Most probiotics lowered the risk of the disease, combinations of bacteria tended to work better than single types, and the specific product mattered a great deal.

Why this question matters so much

Babies born many weeks early face a long list of challenges, and prematurity remains one of the biggest causes of death in young children around the world [1]. One of the most feared complications in a neonatal intensive care unit (NICU) is necrotizing enterocolitis, usually shortened to NEC. In NEC, part of a premature baby's intestine becomes inflamed and can begin to die. It comes on quickly, can be life-threatening, and sometimes requires emergency surgery. Because NEC is so dangerous and so hard to treat once it starts, doctors have spent decades searching for ways to prevent it in the first place.

This is where probiotics enter the story. A premature baby's intestine is colonized by an unusual and limited mix of bacteria, partly because these babies are born before their gut has matured, spend weeks in hospital, and often receive antibiotics early in life. The idea behind probiotics is simple: if you add helpful bacteria — the kinds a healthy gut would normally contain — you might restore a more protective balance and head off the inflammation that leads to NEC.

It can help to know a little about what NEC looks like, because the signs are part of why the NICU watches feeding so closely. A baby developing NEC may have a swollen or tender belly, may stop tolerating their milk feeds, may have blood in their stool, or may simply seem unwell in ways the nurses recognize. The care team monitors these signs carefully, because catching trouble early matters. None of this means a probiotic is a cure — it is a preventive measure meant to lower the odds that NEC develops at all, working quietly in the background alongside everything else the team does.

The long road to an answer

The idea has been tested many times, with confusing results. Some early studies were very promising. One trial gave a mixture of three helpful bacteria to babies weighing under about 3.3 pounds and found much less NEC [2]. A larger study across several hospitals in Taiwan also found that probiotics reduced both how often NEC occurred and how severe it was [3].

But then other carefully designed studies found no benefit at all. A major British trial testing one specific strain of bacteria across two dozen hospitals found that it did not lower NEC, infections, or deaths [4]. Another large trial reduced NEC but did not achieve its main goal of reducing bloodstream infections [5]. These mixed results left families and doctors understandably uncertain. The likely explanation is that "probiotics" is not one thing — different products contain different bacteria at different doses, and they may not all work the same way.

How researchers compared everything at once

To cut through the confusion, the 2025 study used a method called a network meta-analysis [6]. Think of it as a tournament: even when two products were never tested directly against each other, the method uses the trials that do exist to estimate how each one would likely perform, and then ranks them. The researchers, based in China, gathered 51 trials from 19 countries and sorted the treatments into 15 groups — single bacteria like Lactobacillus, combinations of two or three types, and related products. In most of the trials, babies were given the supplement starting on their second or third day of life, once a day, until they went home.

What they found

For preventing NEC and death together, combinations of bacteria came out on top. The single best performer overall was a three-part mix of Bifidobacterium, Lactobacillus, and Enterococcus. When it came specifically to reducing the risk of death, only a few options showed a clear, statistically reliable benefit: Lactobacillus on its own, and two combinations built around Bifidobacterium and Lactobacillus [6]. A separate major study published in 2023 reached a very similar conclusion — that the multi-strain combinations were the ones linked to fewer deaths [7].

The study also found a practical bonus. Lactobacillus helped babies reach full milk feeds sooner — by about two days on average — and shortened their hospital stay by roughly four days [6]. For families, fewer days to full feeding and an earlier trip home are meaningful improvements, even setting NEC aside.

One thing probiotics did not appear to change was the risk of serious bloodstream infection, called sepsis. The study found no evidence that probiotics raised or lowered that risk [6]. That is reassuring on the safety side, but it also means probiotics should not be thought of as an infection-prevention tool.

What this means for your baby

If your baby's NICU offers a probiotic, this research suggests that a multi-strain product — one containing Bifidobacterium and Lactobacillus — has the strongest evidence behind it for reducing NEC and death, and that Lactobacillus may help with feeding and going home sooner. It is worth knowing, though, that the researchers were careful to say their rankings are not the final word. Some of the most eye-catching results came from small trials in which no babies developed NEC at all, which makes the numbers look more dramatic than they may truly be. The benefit for any one baby is real but hard to predict precisely.

It also helps to know that breast milk is itself one of the strongest protectors against NEC, and probiotics are meant to add to — never replace — a mother's own milk. Major expert groups have been deliberately careful here. A respected review of all the evidence concluded that probiotics probably reduce NEC, death, and serious infection, but rated the certainty as only low to moderate and called for more high-quality trials [8]. A European panel of specialists recommended specific strains rather than endorsing probiotics across the board, precisely because the product matters [9]. Individual trials continue to disagree — one study of a Bifidobacterium and Lactobacillus mixture found clear benefit [10] — which is exactly why pooling all the evidence is so useful.

If you want to discuss this with your baby's team, a few simple questions can help. You might ask whether the unit uses a probiotic routinely, and if so, which one and why; whether your baby's gestational age and feeding plan make them a good candidate; and how the team watches for the rare risk of an infection from the probiotic itself. There are no wrong questions here, and most NICU teams welcome them — these are exactly the trade-offs they weigh every day.

The most important takeaway for a worried parent is this: probiotics are a promising, generally safe tool that the strongest evidence supports for many premature babies, especially when a well-chosen multi-strain product is used alongside breast milk. The decision is one to make together with your baby's neonatal team, who can weigh your baby's gestational age, feeding, and overall condition. It is reasonable for different hospitals to make slightly different choices, because the evidence — while pointing clearly toward combination products — still leaves room for judgement, and because the safest, most protective product is only useful if a unit can be confident in its quality and watch carefully for side effects.

What researchers are working on next

The clearest next step is to test the best-performing products directly against one another in large, carefully run trials, using the same definitions and doses everywhere, so that rankings become firm recommendations. Researchers also want to look more closely at which babies — by how early they were born — benefit most, and to keep a close watch on the safety of giving live bacteria to the most fragile infants. Researchers are also paying closer attention to making the products themselves more reliable, so that the helpful bacteria a baby receives are exactly what the label promises, in the right amounts and free of contamination. For now, this study gives families and doctors a clearer map than they have ever had, pointing fairly consistently toward combination products, even if the journey toward complete certainty is not quite finished.

References

  1. Cao G, Liu J, Liu M. Global, Regional, and National Incidence and Mortality of Neonatal Preterm Birth, 1990-2019. JAMA Pediatr. 2022;176(8):787-796. doi:10.1001/jamapediatrics.2022.1622 ↩
  2. Bin-Nun A, Bromiker R, Wilschanski M, et al. Oral probiotics prevent necrotizing enterocolitis in very low birth weight neonates. J Pediatr. 2005;147(2):192-196. doi:10.1016/j.jpeds.2005.03.054 ↩
  3. Lin HC, Hsu CH, Chen HL, et al. Oral probiotics prevent necrotizing enterocolitis in very low birth weight preterm infants: a multicenter, randomized, controlled trial. Pediatrics. 2008;122(4):693-700. doi:10.1542/peds.2007-3007 ↩
  4. Costeloe K, Hardy P, Juszczak E, Wilks M, Millar MR. Bifidobacterium breve BBG-001 in very preterm infants: a randomised controlled phase 3 trial. Lancet. 2016;387(10019):649-660. doi:10.1016/S0140-6736(15)01027-201027-2) ↩
  5. Jacobs SE, Tobin JM, Opie GF, et al. Probiotic effects on late-onset sepsis in very preterm infants: a randomized controlled trial. Pediatrics. 2013;132(6):1055-1062. doi:10.1542/peds.2013-1339 ↩
  6. Dai Y, Yu Q, Zhang F, Ma K, Yan X, Chen W, Chen X, Li S, Han S. Effect of probiotics on necrotizing enterocolitis in preterm infants: a network meta-analysis of randomized controlled trials. BMC Pediatr. 2025;25(1):237. doi:10.1186/s12887-025-05469-z ↩
  7. Wang Y, Florez ID, Morgan RL, et al. Probiotics, Prebiotics, Lactoferrin, and Combination Products for Prevention of Mortality and Morbidity in Preterm Infants: A Systematic Review and Network Meta-Analysis. JAMA Pediatr. 2023;177(11):1158-1167. doi:10.1001/jamapediatrics.2023.3849 ↩
  8. Sharif S, Meader N, Oddie SJ, Rojas-Reyes MX, McGuire W. Probiotics to prevent necrotising enterocolitis in very preterm or very low birth weight infants. Cochrane Database Syst Rev. 2023;(7):CD005496. doi:10.1002/14651858.CD005496.pub6 ↩
  9. van den Akker CHP, van Goudoever JB, Shamir R, et al. Probiotics and Preterm Infants: A Position Paper by the ESPGHAN Committee on Nutrition and the ESPGHAN Working Group for Probiotics and Prebiotics. J Pediatr Gastroenterol Nutr. 2020;70(5):664-680. doi:10.1097/MPG.0000000000002655 ↩
  10. Braga TD, da Silva GAP, de Lira PIC, de Carvalho Lima M. Efficacy of Bifidobacterium breve and Lactobacillus casei oral supplementation on necrotizing enterocolitis in very-low-birth-weight preterm infants: a double-blind, randomized, controlled trial. Am J Clin Nutr. 2011;93(1):81-86. doi:10.3945/ajcn.2010.29799 ↩