Table 1.

Commonly recognized etiologies and pathways leading to spontaneous preterm birth

Pathway	Examples	Mechanistic Effectors	Gestational Age When Predominant
Infection or Inflammation	Intrauterine Lower genital tract Systemic	Pro-inflammatory cytokine/ prostaglandin cascade Matrix metalloproteinases	Early preterm birth (24-32 weeks)
Decidual Hemorrhage	Thrombophilias, Placental abruption Autoantibody syndromes	Thrombin Matrix metalloproteinases	Early or late preterm birth
Maternal/Fetal HPA Activation	Stress	Maternal/Fetal HPA activation Placental CRH Estrogens Immune modulation	Late preterm birth (32-36 weeks)
Pathologic Uterine Overdistension	Multifetal gestation Polyhydramnios	Expression of gap junctions proteins Prostaglandins Oxytocin receptors	Late preterm birth