Mortality rates for extremely low birth weight infants born in Japan in 2005.

OBJECTIVE: Our goal was to investigate the neonatal mortality rate and the mortality rate during the NICU stay for extremely low birth weight infants born in Japan in 2005.

METHODS: The Committee of Neonatal Medicine of the Japan Pediatric Society retrospectively surveyed the deaths of extremely low birth weight infants born and hospitalized between January 1 and December 31, 2005. From 297 institutions in Japan, data on 3065 extremely low birth weight infants, which represented 98.4% of those reported in the maternal and health statistics of Japan in 2005, were collected.

RESULTS: The neonatal mortality rate and the mortality rate during the NICU stay were 13.0% and 17.0%, respectively, which were lower than 17.7% and 21.5% in the survey in 2000. The neonatal mortality rates and the mortality rates during the NICU stay were 53.3% and 67.7% in the <400-g birth weight group (n = 62), 42.1% and 53.5% in the 400- to 499-g birth weight group (n = 159), 22.2% and 27.7% in the 500- to 599-g birth weight group (n = 387), 16.8% and 22.2% in the 600- to 699-g birth weight group (n = 537), 9.4% and 12.7% in the 700- to 799-g birth weight group (n = 574), 6.3% and 9.1% in the 800- to 899-g birth weight group (n = 649), and 3.9% and 5.3% in the 900- to 999-g birth weight group (n = 697), respectively. The factors involved in the deaths of extremely low birth weight infants included lower gestational age, lower birth weight, male gender, multiple birth, institutions in which <10 extremely low birth weight infants were admitted per year, and no prenatal maternal transfer.

CONCLUSION: The mortality rates of extremely low birth weight infants who were born in 2005 demonstrated definite improvement.