ObjectiveTo analyze the placental histology in cases of preterm premature rupture of membranes (PROM), classify the cases according to the results of the histologic examination, and determine if these histologic groups have different clinical characteristics and outcomes.MethodsDuring a 3-year period, a cohort of 235 women with preterm PROM was studied prospectively. The women were classified according to placental histologic findings, and their prenatal and intrapartum courses and perinatal mortality and morbidity were analyzed and compared.ResultsOne hundred two placentas (43.4%) exhibitied acute inflammatory lesions, 48(20.4%) had vascularlesions, 48(20.4%) had both inflammatory and vascular lesions, (13.2%) had no abnormal findings, four (1.7%) had villous edema, and two (0.8%) had chronic villitis. The four largest histologic groups had distinctive characteristics with respect to gestational age at the time of PROM and at delivary, duration of the latency period, and perinatal mortality and morbidity.ConclusionCases of preterm PROM may be classified according to placental histologic findings, and these groups have different clinical manigestations, prognoses, and outcomes.