Of the 1433 subjects in the original glutamine trial, 1272 infants met the inclusion criteria established for this study. Of the 161 infants who were excluded from the analyses: 32 died within the first 72 h of life; 7 infants were discharged or transferred to another institution before age 14 days; 7 had either gut or heart malformations; and 16 infants were <23 weeks gestation. An additional 99 infants either developed NEC (n
= 31) or died (n
= 68) within the first 14 days of life and were not included in the analyses. Among the 99 infants who developed NEC or died before 14 days, 46.9% (n
= 46) received some enteral feeding before the outcome. Of these, 32% (n
= 32) received some HM in the first 14 days of life (mean (s.d.) cumulative volume of HM received 119.6 ml kg–1
(190.7)), and 25.3% (n
= 25) received some formula (cumulative volume of formula received 127.7 (160.6) ml kg–1
). Among the 1272 infants included in this study, 173 (13.6%) either died (n
= 75) or developed NEC (n
= 98) after day 14 of life, with the mean (s.d.) age of NEC onset or death of 37 (19) days. Most study infants (91%, n
= 1153) received some enteral feeding within the first 14 days of life: 31.6% (n
= 402) received HM only, 28.3% (n
= 360) received formula only, 30.7% (n
= 391) received a combination of HM and formula and the remaining 9.4% (n
= 119) received no enteral nutrition. There was no association between the amount of HM received in the first 14 days and whether or not the infant received glutamine supplementation as part of the original clinical trial (P
= 0.57). There was also no association with glutamine treatment group and NEC.16
Therefore, glutamine supplementation was not included in any of the statistical models.
Aspects of care, including feeding practices, varied from center to center. Among infants who had a PDA, the proportion of infants treated with indomethacin ranged from 70 to 100%, whereas the proportion of infants who had a ligation ranged from 5.6 to 65.2%. The proportion of infants who received any HM ranged from 36.8 to 94.7%. The incidence of NEC varied by center and ranged from 0 to 12.7%.
The characteristics of the study infants and the unadjusted associations between enteral feeding and NEC or death are summarized in . Compared to infants who survived free of NEC, infants with NEC or death were fed less HM (mean (s.d.)) cumulative volume (85 (154) vs 154 (250) ml kg–1), and had a lower mean daily HM intake 6 (11.0) vs 11 (17.9) ml kg–1 per day) during the first 14 days of life. Over the entire NICU stay, infants who died or developed NEC had a lower mean proportion of total intake as HM (6 (10) vs 10% (16)). Infants with NEC or death were also more likely to receive parenteral nutrition as their only nutritional intake during the first 14 days of life compared to infants who did not develop NEC or death (19 vs 7.8%).
Characteristics of study infants grouped by outcome
The results of the multivariable Cox analyses, reported as adjusted HRs and 95% CIs, are shown in . Controlling for birth weight, small for gestational age, race, antenatal steroids, receipt of mechanical ventilation, PDA and center, the HR for NEC or death after age 14 days was 0.87 for every 100 ml kg–1 increase in the volume of HM. In other words, the hazard of NEC or death was decreased by 13% for every 100 ml kg–1 increase in HM an infant received in the first 14 days of life. As illustrated in , increasing amount of HM intake within the first 14 days of life was associated with increased survival time free of NEC.
Results from proportional hazards models for time to NEC or death
Figure 1 Adjusted survival curves for necrotizing enterocolitis (NEC) or death by amount of human milk (ml kg–1) over the first 14 days of life. Survival curves adjusted for birth weight, small for gestational age, race, patent ductus arteriosus (PDA), (more ...)
The results of the multivariable model that only included infants who received some HM in the first 14 days (n = 792), each 100 ml kg–1 increase in the cumulative amount of HM fed was associated with a decreased risk of NEC or death, indicating a dose–response relationship (HR 0.87, 95% CI 0.77, 0.97).
An increasing proportion of HM to total intake (enteral plus parental) was also associated with a decreased relative risk of NEC (HR 0.83, 95% CI 0.72, 0.96). As illustrated in , increasing proportion of HM to total intake was associated with increased survival time free of NEC. When focusing on enteral feeding only, there appeared to be a trend towards a decreased risk of NEC or death among infants who received 100% HM as a proportion of total enteral intake (HM plus formula). However, this finding was not statistically significant (HR 0.85 (95% CI 0.60, 1.19)).
Figure 2 Adjusted survival curves for necrotizing enterocolitis (NEC) or death by proportion of human milk to total intake over the first 14 days of life. Survival curves adjusted for birth weight, small for gestational age, race, patent ductus arteriosus (PDA), (more ...)