All of the accumulated evidence regarding probiotics in preterm infants to prevent necrotising enterocolitis (NEC) clearly shows that probiotic bacteria (specifically bifidobacteria and lactobacilli) are effective in reducing the incidence of NEC by more than 50%, they, as a result, reduce mortality in eligible infants.
Do these benefits from randomized controlled trials translate into real benefits in routine use? It seems highly likely that they should, especially as there is no evidence of any harm in any of the randomized trials.
Cohort studies are one way of keeping track of the effects of an intervention when actually introduced into daily use. Such studies are better if designed prospectively (as you can determine definitions etc more precisely) and better if inception cohorts, that is they include all patients who are eligible from the moment they become eligible.
A newly published study was a retrospective cohort, (Bonsante F, Iacobelli S, Gouyon JB. Routine Probiotic Use in Very Preterm Infants: Retrospective Comparison of Two Cohorts. Am J Perinatol. 2012(EFirst). Epub 2012/07/10. https://www.thieme-connect.com/DOI/DOI?10.1055/s-0032-1321498) from an NICU in France. The authors showed that in routine use in infants of 24 to 31 weeks gestation, Lactobacillus rhamnosus was associated with a decrease in NEC of 80%, and a decrease in mortality of 54%. The same order of effect that has been seen in the RCTs.
More confirmation of the benefits of probiotic bacteria in preterm infants, as if more were needed!