[Prenatal risk factors for neonatal asphyxia: how risk for each?]. 
Neonatal asphyxia is the third leading cause of neonatal death and main cause of long-term neurodevelopmental handicap throughout the world.  Prevention is more important than treatment.  Most previous reports are limited to retrospective investigations of the relationships between some prenatal risk factors and low Apgar scores.  This study was designed to prospectively investigate the relationship between prenatal risk factors and neonatal asphyxia and the influence of single or multiple risk factors on the incidence of neonatal asphyxia, and examine significant risk factors for neonatal asphyxia.  From April 2002 through October 2004, a total of 10 376 live-born newborns were enrolled.  Forty-six prenatal risk factors were investigated.  Neonatal asphyxia was diagnosed based on the following four items: 1.  1-min Apgar score <or=7; 2.  Umbilical artery blood pH<7.20; 3.  At least one organ had evidence of asphyxial injury; 4.  Other causes of low Apgar score were excluded.  The number, the constituent ratio and the exposure frequency of newborns with single or multiple risk factors were counted.  The influence of risk factors on the incidence of asphyxia was analyzed.  The significant risk factors were screened by single logistic regression analysis and forward stepwise conditional multiple logistic regression analysis, with enrolled threshold alpha<or=0.05, excluded threshold alpha>or=0.10 and p<0.05 as significant.  The OR and 95%CI were calculated for each significant risk factor.  Of the 10 376 newborns, 8 530 cases (82.21%) had 1-9 risk factors, and asphyxia occurred in 117 cases (1.13%) out of the 8 530 cases.  In the 1 846 cases without risk factors, none had asphyxia (x2=25.6, p<0.01).  The incidence of asphyxia increased with increasing numbers of risk factors, from 0.23% in newborns with one risk factor to 14.29% in newborns who had nine risk factors (r=0.96, p<0.01).  Twelve significant risk factors identified were as follows: ominous fetal heart rate patterns (OR=17.1,95%CI:11.2-25.9), placenta abruption (OR=15.2, 95% CI: 4.5-51.8), maternal lung diseases (OR=11.5, 95% CI:1.4-91.3), fetal acidosis (OR=6.1, 95% CI:1.5-24.1), placenta previa (OR=5.0,95% CI:1.5-16.9), breech delivery (OR=4.5, 95% CI: 2.1-9.9), meconium stained amniotic fluid (OR=3.2, 95% CI:2.2-4.8), forcepsjassisted delivery (OR=3.2, 95%CI: 1.1-9.9), prolonged labor (OR=2.94, 95%CI:1.5-5.8), abnormal utero contraction (OR=2.8, 95% CI:1.7-4.6), and premature delivery (OR=2.5,95%CI:1.4-4.8).  Cesarean section had a protective effect (OR=0.6, 95% CI:0.4-0.9) (all p<0.05).  It is very important to prevent perinatal asphyxia by systematically examining prenatal risk factors and giving interventions for the newborns with risk factors, especially those with the above significant risk factors or with multiple risk factors.  Proper cesareon section according to indications might be helpful to decrease the incidence of birth asphyxia.