Spontaneous Intestinal Perforations in Extremely Low Birth Weight Infants

I read with interest the article by Fatemizadeh et al [1] describing an increased incidence of spontaneous intestinal perforations (SIP) in their selected cohort. In discussing their findings, I did not find any explanation on why SIP cases were more prevalent in their units? Do they have any management policy or protocol changes during the study period? They did look at the use of vasopressors and indomethacin. However, none of the SIP infants had feeds above trophic feeds which make human milk (HM) less likely to be a cause of SIP.