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

Abstract

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 750 g (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.

Figure 1

Trends in mortality, morbidity, and interventions among the 39 hospitals. Number of infants analyzed was 12,863. (a) Deceased at discharge (filled squares). (b) Indomethacin for PDA, PDA ligation, and symptomatic PDA. Filled squares, indomethacin for PDA; filled triangles, PDA ligation; filled diamonds, symptomatic PDA. (c) IVH grade III or IV, NEC and/or intestinal perforation, and late-onset AOP. Filled squares, IVH III or IV; filled triangles, NEC and/or intestinal perforation; filled diamonds, late-onset AOP. (d) Intravenous hyperalimentation, ROP treatment, and iNO. Filled squares, intravenous hyperalimentation; filled triangles, ROP treatment; filled diamonds, iNO. AOP, adrenal insufficiency of prematurity; iNO, inhaled nitric oxide; IVH, intraventricular hemorrhage; NEC, necrotizing enterocolitis; PDA, patent ductus arteriosus; ROP, retinopathy of prematurity.

Figure 2

Trends in mortality by birth weight and gestational age. (a) Mortality by birth weight. Filled squares, −500 g (P = 0.31); filled triangles, 501–750 g (P = 0.03)*; filled diamonds, 751–1,000 g (P = 0.05); black crosses, 1,001–1,250 g (P = 0.71); filled circles, 1,251–1,500 g (P = 0.44). P values were calculated by the Cochrane–Armitage χ² test. *Significant decrease. (b) Mortality by gestational age. Filled squares, 22–24 wk (P = 0.05)**; filled triangles, 25–27 wk (P = 0.21); filled diamonds, 28–30 wk (P = 0.93); black crosses, 31–33 wk (P = 0.06); filled circles, 34 wk- (P = 0.42). P values were calculated by the Cochrane–Armitage χ² test. **Significant decrease.