Preterm birth is one of the most common obstetric complications. In recent decades, the incidence of premature birth remains high throughout the world, and even shows a rising trend in some countries and areas. Therefore, understanding the mechanisms of human parturition and developing the effective prevention and treatment strategies of premature delivery are urgent to improve maternal and fetal health and overall quality of population. Due to the limitation of ethics and testing methods, the prediction and early diagnosis of premature birth have been the primary problem that perplexes obstetricians. Various body fluids, including amniotic fluid, cervicovaginal fluid, urine, saliva and blood, provide rich sources of putative biomarkers that may be causative or reflective of preterm labor. In recent years, the exploration of novel biomarkers for noninvasive detection is in the ascendant, which sheds new lights for the prediction and early diagnosis of preterm labor. This review compares the biomarkers for the detection of preterm birth, and discusses the future prospect.