The survival rate of infants weighing less than 1,000 g at birth(extremely low birth weight infants, ELBWI) has increased due to recent advances in perinatal and neonatal intensive care. The purpose of this study was to evaluate the survival rates of ELBWI born at Seoul National University Hospital during the last six years.

A total of 99 infants were divided into three groups(period I: 2000 to 2001, period II: 2002 to 2003, period III : 2004 to 2005) based on date of birth. We compared the survival rate of ELBWI over the three periods, using CRIB II score for adjustment for clinical severity.

Overall survival rate of ELBWI was 74.7 percent. The survival rate of ELBWI increased over the three periods(period I: 60.7 percent, period II : 73.3 percent, period III : 85.3 percent). The threshold of viability(defined as survival of at least 50 percent of infants) was 25 weeks of gestation and 600 g at birth. The birth weight-specific survival rates increased considerably over the three periods for infants <750 g at birth(period I: 10 percent, period II: 46.2 percent, period III : 70.6 percent). The survival rates of ELBWI over the three periods increased much remarkably after adjustment for clinical severity by CRIB II score.

In our institution, survival rates of ELBWI during the last six years continued to improve, particularly for infants weighing <750 g at birth. This increase in survival rates was not associated with the clinical severity of ELBWI.