Placental insufficiency is a leading cause of preterm labor

Preterm labor is a multifactorial syndrome with a variety of risk factors. Intra-amniotic infection is one risk factor, but accumulating evidence suggests it is an uncommon cause of preterm labor. Instead, most cases of spontaneous preterm labor appear to be caused by placental insufficiency, similar to preeclampsia and fetal growth restriction. This review addresses the placental findings most commonly observed in preterm labor and discusses the prevalence of these features related to the gestational age at the time of delivery. The implications for clinical management and the long-term health of the infant may be profound.