Survival rate of extremely low birth weight infants and its risk factors: case-control study in Japan.

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 (n = 366) and the controls (n = 1,347). 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.