Probiotics cut death and necrotizing enterocolitis risk in very preterm infants

In 2020, Sweden made a quiet decision that would reshape how doctors treat some of the most fragile patients in medicine. The country's health authorities issued a national recommendation: give probiotics to very preterm infants in neonatal intensive care units. It was a bet on a simple idea—that the right bacteria, introduced early, might protect newborns born too soon from two of the gravest threats they face: death itself, and necrotizing enterocolitis, a devastating intestinal disease that strikes without warning.

Now, four years of real-world evidence from Swedish hospitals has vindicated that bet. Researchers analyzed 4,695 very preterm infants—those born between 28 and 31 weeks of gestation—admitted to Swedish neonatal units between 2017 and 2024. The infants who received probiotics showed a 72 percent lower risk of death or necrotizing enterocolitis combined, compared to those who did not. When the outcomes were separated, the numbers became even more striking: an 84 percent reduction in death risk and a 75 percent reduction in necrotizing enterocolitis risk.

The probiotic regimen itself was straightforward. Infants received one billion colony-forming units of freeze-dried bacteria—a combination of Bifidobacterium infantis, Bifidobacterium lactis, and Streptococcus thermophilus—given daily from birth until 34 weeks of postmenstrual age. The intervention was neither invasive nor expensive. What changed was adoption. Before 2020, no infants in the study cohort received probiotics. By 2020, uptake jumped to 16.9 percent. From 2021 onward, an average of 64.8 percent of eligible infants were receiving the treatment. This natural experiment—a sudden policy shift creating a clear before-and-after—allowed researchers to measure real clinical impact at the population level, not just in controlled trials.

The study enrolled 1,571 infants in the probiotic group and 3,124 in the no-probiotic group. Both groups were comparable in baseline characteristics: mean gestational age of 30.2 weeks, with 45.7 percent female infants. The researchers adjusted their analysis for confounding factors, a statistical safeguard against attributing benefits to probiotics when other variables might be responsible. Even after this adjustment, the protective effect held. The adjusted relative risk for death or necrotizing enterocolitis was 0.28, meaning the probiotic group faced less than one-third the risk of the untreated group.

What made the benefit work? The data suggested that roughly 42 percent of the mortality reduction came through preventing necrotizing enterocolitis—meaning the probiotics were not just keeping infants alive through one mechanism, but through multiple pathways. A healthier gut, it seemed, meant a healthier infant overall. One outcome, however, showed no difference: culture-proven sepsis, a bloodstream infection, occurred at similar rates in both groups. The probiotics were not a universal shield, but they were protective where it mattered most.

These findings carry weight because they come from an entire nation's experience, not a single hospital or a carefully selected trial population. Swedish neonatal units serve a diverse population across urban and rural settings, teaching hospitals and smaller facilities. The consistency of the benefit across this real-world landscape suggests the effect is robust and likely to translate to other healthcare systems. For parents of very preterm infants—babies born months before their due date, fighting for survival in incubators—the implications are direct: a simple, safe intervention might mean the difference between coming home with their child or leaving the hospital without them.