Probiotic supplementation in very preterm babies was linked to a lower risk of both severe intestinal disease and death. This is shown by a new study from the Karolinska Institutet, published in JAMA Network Open. The findings are based on data from nearly 4,700 babies born prematurely in Sweden.

Very preterm babies are at increased risk of developing necrotising enterocolitis (NEC), a serious intestinal disease that can be life-threatening. Since 2020, the Swedish Neonatal Society has recommended that babies born between gestational weeks 28 and 31 receive daily probiotic supplements – that is, live bacteria that can influence the gut microbiota. This is in line with a European recommendation based on international research.

In the current study, the researchers analysed data from the Swedish nNeonatal care quality register on 4,695 babies born between 2017 and 2024. Of these, 1,571 babies received a probiotic supplement containing three selected bacterial strains, whilst 3,124 babies did not. The researchers investigated whether probiotic supplements could be linked to the risk of death or of developing NEC during their stay in the neonatal ward.

”We found that infants who received probiotics had a significantly lower risk of both NEC and death compared with those who did not receive the supplements. At the same time, mortality was low in both groups,” says Ayoub Mitha, a doctor and researcher at the Department of Medicine, Solna, Karolinska Institutet, who is the study’s corresponding author.

Among children who received probiotics, 0.8 per cent experienced death or NEC, compared with 3.4 per cent among those who did not receive the supplement. The risk of death was 0.3 per cent in the probiotic group compared with 1.4 per cent in the group without probiotics. The risk of NEC was 0.6 per cent and 2.5 per cent respectively.

The researchers used several different statistical methods to account for differences between the groups. The results were similar regardless of the analysis method. Further analyses suggested that a significant proportion of the lower mortality rate was linked to fewer children developing NEC.

However, the researchers found no clear link between probiotic supplementation and the risk of sepsis, a serious infection that can spread throughout the body. The proportion of children affected by sepsis was roughly the same in both groups.

“Our findings contribute to the international body of knowledge and may help healthcare professionals and families make informed decisions regarding probiotic supplements for very preterm infants. At the same time, it is important not to generalise the results to extremely preterm infants—those born before 28 weeks—as this group was not included in the study,” says Ayoub Mitha.

The researchers also emphasise that the study is observational. This means that it can show associations but cannot definitively establish cause and effect.

See the study for details of funding and any conflicts of interest.