Abstract： Objective To investigate factors and neonatal outcomes associated with histologic chorioamnionitis (HCA) in preterm premature rupture of membranes (PPROM).Methods From Jan.2008 to Jun.2011,230 women with PPROM at 28 -33 +6 weeks of gestation undergoing deliveries in the Second Affiliated Hospital of Wenzhou Medical College were studied retrospectively.According to placental histopathologic findings,those patients were categorized into two groups,including 138 cases in histologic chorioamnionitis (HCA group ) and 65 cases in non-chorioamnionitis (control) group.Age,parity,gestational age of PPROM and delivery,latency period,oligohydramnios,white blood cell (WBC) count and serum C-reactive protein (CRP) level at admission and before delivery,the incidence of neonatal respiratory distress syndrome (NRDS),neonatal pneumonia,bronchopulmonary dysplasia,necrotizing enterocolitis,early-onset neonatal sepsis,abnormal brain sonography findings and mortality were compared between two groups.Results ( 1 ) The incidence of HCA was 68.0.％ ( 138/203 ) in all 203 cases with PPROM.(2) The occurring ruptured membrane gestation in HCA group was ( 31.1 ± 1.5 ) weeks,which were significantly earlier than (32.0 ± 1.3 ) weeks in control group ( P ＜ 0.05 ).The level of CRP of (8.2 ± 14.9) mg/L before delivery in HCA group was significantly higher than (5.5 ±7.2) mg/L in control group (P ＜ 0.05).The rate of oligohydramnios and cesearean sections were 55.1％ (76/138) and 45.7％ (63/138) in HCA group,which were significantly higher than 30.8％ (20/65) and 29.2％ (19/65) in control group (P ＜0.05).There were no significant difference in patient's age,parity,WBC count and CRP at admission between two groups (P ＞ 0.05 ).The latency period did not show significant difference between (140± 116) hours in HCA group and (129 ± 125) hours in control group (P ＞ 0.05).(3) Using multivariable logistic regression models,oligohydramnios ( OR =2.937 ),gestational age of PPROM ＜ 32 weeks ( OR =2.352),serum CRP level ＞ 8 mg/L before delivery ( OR =4.923 ) and latency period ＞ 48 -168 hours (OR =4.439) were significantly associated with HCA (P ＜0.05).(4) The gestational age of delivery and birth weight of HCA group were significantly lower than those of control group [ ( 32.0 ± 1.5 ) weeks vs.( 32.7 ± 1.5 ) weeks,( 1680 ± 379) g vs.(2017 ± 333) g,respectively,P ＜ 0.05 ].The incidence of Apgar ＜7,abnormal brain sonograhy findings, neonatal pneumonia,bronchopulmonary dysplasia,early-onset neonatal sepsis and mortality in HCA group were significantly higher than those in control group [20.3％ (28/138) vs.7.7％ (5/65),14.5％ (20/138) vs.4.6％ (3/65),12.3％ (17/138) vs.3.1％(2/65),5.8％ (8/138) vs.0,6.5％ (9/138) vs.0,12.3％ (17/138) vs.3.1％ (2/65),respectively,P ＜ 0.05 ].The incidence of necrotizing enterocolitis ( 1.5％,2/138 ) in HCA group was higher than that of controlgroup(0) and the incidence of NRDS ( 18.8％,26/138) in HCA group did not show statistical difference with 21.4％ ( 14/65 ) in control group ( P ＞ 0.05 ).Conclusions It was found that HCA was significantly correlated with lower gestational age of PPROM,higher serum CRP level before delivery,prolonged latency period and oligohydramnios in PPROM.HCA could increase the neonatal morbidity and mortality.