In 2010, a 1∶1 case-control study on preterm birth in five counties in western China had been carried out supported by WHO to learn the main causes on preterm in rural areas so as to intervene in the future.There were 459 pairs subjects got investigation by questionnaire to learn general situation, pregnancy history, reproductive health infection (RTI) symptoms, pregnancy complications, et al.The case group was pregnant women of preterm birth, and control group was 1:1 matched pregnant women of normal delivery.