This study developed a set of histologic features that will allow subclassification of placentas with preterm premature rupture of membranes. Placentas were obtained from patients participating in a multi-institutional NICHD Maternal-Fetal Medicine Unit Network study of antimicrobial therapy after preterm premature rupture of membranes. The rupture site was sampled by inking the open sac margin and rolling a membrane strip in four quadrants from the ink to the placental margin. Independently, four pathologists used a provisional feature list to score the slides from 15 placentas. A concordance analysis was performed on those results. With those results, the slides were reviewed concurrently to discover the source of disagreements and to revise the feature list. The sampling method frequently demonstrated a rupture site with histology distinct from that of the remainder of the membranes. After review of the preliminary scoring results, 29 features of membrane histology present in preterm premature rupture could be objectively described with agreement among four pathologists. The feature list allows both novel and commonly recognized histologic features of fetal membranes to be recorded with objectivity. This list, with the described sampling technique, is presented as a tool for clinical correlation in studies of membrane rupture, especially in preterm, premature rupture.