Abstract： Objective To investigate the incidence and relevant information of preterm birth and the outcomes of preterm infants delivered at various gestational weeks and for different causes. Methods Totally 955 women, who ended their pregnancies before term, and 1066 neonates of the previous mothers were enrolled in this survey, among 15 197 deliveries at Peking University First Hospital, Beijing Gynecological and Obstetric Hospital, Women's and Children's Hospital of Haidian District and Peking University Third Hospital, respectively, from December 1~(st), 2006 to May 31~(st), 2007. Results (1)Incidence of preterm birth: The overall incidence of preterm birth of the 4 hospitals was 6. 3% (955/15 197), and it was 8.1% (125/1549) in Peking University First Hospital, 13.1% (150/1142), which was the highest (P<0.01), in Peking University Third Hospital, 5.5% (369/6656) in Beijing Gynecological and Obstetric Hospital and 34.0% (311/5850) in Women's and Children's Hospital of Haidian District.The preterm birth rate at the two comprehensive hospitals was significantly higher than that of the two specialized hospitals [10.2% (275/2691) vs 5.4% (680/12 506), P <0.01]. (2) Gestational weeks at delivery: The incidence of preterm birth before 34 weeks was 28.5% (272/954) and the number changed to 71.5% (682/954)for those preterm deliveries after 34 weeks. However, this number varied among the 4 hospitals. Peking University First Hospital had the highest incidence of preterm birth before 34 weeks(P< 0.05), and the lowest was found in Women's and Children's Hospital of Haidian District(P<0.01), but no difference was found between Peking University Third Hospital and Beijing Gynecological and Obstetric Hospital. (3) Etiology of preterm birth: Preterm premature rupture of membranes (PPROM) accounted for the most proportion of all preterm birth cases, followed by iatrogenic preterm birth and spontaneous preterm birth. But the causes of preterm birth in the 4 hospitals were different. Peking University Third Hospital had a higher incidence of iatrogenic preterm birth than the others (P<0.01), and Peking University First Hospital had a higher incidence of preterm birth caused by PPROM and lower incidence of spontaneous preterm birth. The first four reasons of iatrogenic preterm birth were preeclampsia (143, 42.0%), fetal distress (58, 17.1%), placenta previa (43, 12.6%) and placenta abruption (33,9.7%). (4) Neonatal outcomes in different hospitals: The neonatal outcomes were quite different among the 4 hospitals due to different causes and different delivery weeks. The highest neonatal mortality rate was found in Beijing Gynecological and Obstetric Hospital (5.4%, 22/408) compared to that in Women's and Children's Hospital of Haidian District (1.3%,4/320) and Peking University Third Hospital (0. 6%, 1/170) (P< 0.01), but without any difference when compared to that in Peking University First Hospital (2.4%, 3/ 124) (P>0.05). (5) Neonatal outcomes at different gostational age: The recovery rate of preterm infants delivered at <32 weeks was lower than those delivered ≥32 weeks (P<0.01), and this number rose to 99. 6% in those delivered ≥34 weeks. More infants delivered <32 weeks were given up for treatment or died during the perinatal period than those delivered ≥32 weeks, with the neonatal mortality rate of 22.1% for those delivered at <32 weeks and only 0.3% for those delivered at ≥ 34 weeks (P<0.01). (6) Neonatal outcomes for various causes: The premature neonatal mortality rate for iatrogenic preterm births was higher than that of PPROM (4.9% vs 1.6%, P<0.05). But the neonatal recovery rates were similar among the PPROM, spontaneous and iatrogenic preterm birth group (P>0.05). Conclusions Preterm birth is associated with high perinatal mortality rate, especially for those delivered before 32 weeks which would be highlighted in prevention. Reduction of the iatrogenic preterm birth, combined with proper prevention of PPROM, is an important issue in decreasing the prevalence of preterm birth.