Preterm Labor, a Syndrome Attributed to the Combination of External and Internal Factors.

Preterm labor (before 37 weeks' gestation) is the leading cause of neonatal mortality and morbidity, which can be divided into iatrogenic preterm labor, infectious preterm labor, and spontaneous preterm labor (sPTL). Up to now, there continue to be great difficulties in prediction and prevention of sPTL, owing to multiple risk factors, pathogenesis, and pathologic processes contributing to the event, which have not been fully clarified. Pregnancy maintenance and parturition is a complicated process with continuous maternal-fetal dialogue, in which both maternal and fetal factors participate and affect the outcome of pregnancy, including sPTL. Besides, external factors can also participate in sPTL, individually or through the interaction with internal factors. In this article, we summarize recent studies regarding sPTL from our and other groups, and discuss the risk factors and pathogenesis of preterm birth from both external and internal (maternal and fetal) aspects, so as to provide theoretical evidences for the diagnosis, prevention, and treatment of sPTL in the future.