Preterm birth can be categorized as medically indicated
(when pregnancy is interrupted at preterm
gestations for maternal or fetal indications) and
spontaneous (onset of labor before or after membrane
rupture at preterm gestations). More than
one half of PTBs due to medical indications are on
the basis of conditions associated with ischemic
placental disease including preeclampsia, fetal
distress, small-for-gestational-age (SGA), and placental
abruption (Ananth & Vintzileos, 2006).