Trends in morbidity and mortality among very-low-birth-weight infants from 2003 to 2008 in Japan

BACKGROUND: Although medical care for very-low-birth-weight (VLBW) infants has improved over time, it is unclear how this has affected mortality and morbidity. To characterize these trends, a network database was analyzed. METHODS: This is a cohort study of VLBW infants born from 2003 through 2008. RESULTS: Over the 6-y period, 19,344 infants were registered and analyzed. Crude mortality rates among the infants at discharge decreased significantly (from 10.8 to 8.7%) during the study period. The greatest improvement in mortality was observed among infants with birth weights between 501 and 750g (25.6-17.7 %). The odds ratio (OR) of mortality over year adjusted for potential confounders by a logistic regression model was 0.94 (95% confidence interval 0.92-0.97). Significant increases were observed in some morbidities, including symptomatic patent ductus arteriosus with an OR of 1.11 (1.09-1.13); late-onset adrenal insufficiency, 1.21 (1.17-1.26); and necrotizing enterocolitis/intestinal perforation, 1.10 (1.01-1.12). However, the severe form of intraventricular hemorrhage, with an OR of 0.98 (0.92-0.99), decreased significantly. Risk-adjusted trends in other morbidities showed no significant change. CONCLUSION: Mortality of VLBW infants decreased significantly over the 6-y study period. Decreasing morbidity is essential for further improvement in the outcomes in VLBW infants.