Necrotizing Enterocolitis remains a devastating disease. One of the major causes of mortality in Very Low Birth Weight Infants, it often strikes when babies are starting to do well. Because it is relatively unpredictable, observational studies are potentially useful, but can easily be misleading. In particular, observational studies which are performed as a result of a perceived change in incidence might easily be biased.
One recent study that was published has received some publicity, I myself received some links on Linked-In pointing to this study, which at first sight seems to show that advancing feeds slowly might decrease NEC. Lets examine the data a bit more carefully.
In 2009 a hospital changed their feeding policies. A paper published in 2014 reported their data from 2009 to 2012. According to the published article the paper was received on July 24th 2014, and accepted on August the 5th. Which immediately makes me wonder two things, why the authors decided to perform this study, and how do they get a paper accepted so quickly? If the authors performed the study because they saw a decrease in NEC, and then decided to do the analysis, that immediately creates a bias, many other hospitals could possibly have made a similar change and not noted any change in NEC, and therefore not looked at their data. Studies such as this are more likely to be reliable if the decision to prospectively collect and try to publish their data is made at the time that the change in therapy is introduced. But then a similar study showing no effect on NEC would be very difficult to publish, and probably not be accepted in under 2 weeks!
There are a couple of concerning things in their findings, one is that after the change in the protocol there was not actually statistically any less NEC overall than before the change in protocol. Only by a subgroup analysis, was the group of babies under 750g significant, and then they did not report the p-value of the interaction, which is really essential. They showed much less NEC in the babies under 750 g birth weight than those between 750 and 1000g. Which really strongly suggests to me that this is just the result of the random nature of NEC incidence, I don’t know any large study that has ever found more NEC in the larger babies.
More worryingly, the new protocol led to babies having later commencement of feeds, longer use of intravenous nutrition, longer use of picc lines, and really horrendous nutritional outcomes, with over half of the babies being under the 10th percentile at discharge (admittedly that was better than the 75% with their older protocol). The feeding protocol that they introduced is entirely non-evidence based, as I have noted before here, there is no evidence from controlled trials that varying the advancement of feeds has any effect at all on the incidence of NEC.
A slightly older study (from 2009) provides interesting data from the German Neonatal Network, and is, I think, much more reliable. They compared the outcomes of babies from centers where it took on average less than 12.5 days to get their VLBW babies on full feeds, to centers where it took on average more than 12.5 days to get the babies to full feeds.
You can see here the clinical outcomes from the study. The only things that were different between the groups were the late-onset sepsis, which was much higher in the babies with slower feeding. Surgical NEC was slightly (non-significantly) more frequent with slower feeding, and severe retinopathy was also higher, which is entirely consistent with the recent information linking retinopathy with poorer nutrition.