Aim. To clarify the effect of perinatal events on the survival of ELBW infants in Japan. Methods. 1,713 ELBW infants, from 92,630 live births in 2001 and 2002, born at 22–36 weeks of gestation were registered. Case was defined as death at discharge. The relevant variables were compared between the cases ( ) and the controls ( ). Results. The total survival rate was 78.6%. There was a significant difference between the survival rate in cesarean and vaginal delivery at 24–31 weeks of gestation. Cesarean delivery in infants with a birth weight >400？g was significantly advantageous to the survival rate of ELBW infants than vaginal delivery. The significant contributing factors were gestational age at delivery (OR: 0.97), Apgar score at 5？min (0.56), antenatal steroid (0.41), and birth weight (0.996). Nonvertex presentation (1.81), vaginal delivery (1.56), and placental abruption (2.50) were found to be significantly associated with neonatal death. Conclusions. Cesarean section might be advantageous for survival in ELBW infants over 24 gestational weeks or 400 grams of birth weight. Nonvertex presentation, vaginal delivery, and placental abruption could be significant risk factors for survival of ELBW infants. 1. Introduction Prematurity is a particularly significant risk factor for survival of the neonate and is associated with increased perinatal mortality. The prognosis of low birth weight (LBW) infants has been improved drastically with advances in perinatal medicine. More than 80% of infants survive delivery at 24 weeks of gestation in many perinatal centers in Japan [1]. Interest has now turned to improvement of the intact survival rate of extremely low birth weight (ELBW) infants. To save the lives of ELBW infants, particularly those born at 22-23 gestational weeks, is thought to be at the frontier of current perinatal medicine. Gestational weeks 22 to 23 seem to be a limit of viability. There are many perinatal factors that might influence the prognosis of ELBW infants. It has been well known that antenatal steroid administration improves the prognosis as well as survival [2], whereas vaginal delivery in nonvertex presentation is an adverse factor [3–5]. However, indication of cesarean section in extremely preterm infants less than 24 weeks is a matter of wide debate. This debate is also of great importance in Japan. To reach a conclusion, a nationwide survey in Japan is needed. The World Health Report 2005 stated that the neonatal mortality rate within 28 days was 1.8 per 1000 live births in Japan, which was the next best data after Singapore (1.1
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