Objectives: Preterm premature rupture of membranes (PROM) accounts for 30-40% of all preterm births. The objectives of this study were to determine whether matrix metalloproteinase-9 (MMP-9) is increased in preterm PROM fetal membranes, whether labor or gestational age affects expression, and whether the increase is localized to the rupture site or is membrane-wide.
Methods: Fetal membranes were collected from 15 pregnancies complicated by preterm PROM and 26 control cases, which delivered at term or preterm without PROM. The preterm PROM cases represented both patients who labored and those who did not. Membrane samples at the rupture site and a remote site (approximately > 5 cm) were analyzed for MMP-9 protein and enzymatic activity by Western blot and gelatin zymography, respectively.
Results: MMP-9 levels in fetal membranes were similar at both the rupture and the remote sites. The highest levels of total MMP-9 protein were found in preterm PROM patients with labor (p < 0.05) and were increased four-fold over protein levels in non-laboring preterm PROM patients delivered by Cesarean section (p < 0.001). In preterm PROM patients without labor, levels of MMP-9 protein were similar to those of non-laboring patients at term and preterm. Zymography correlated with protein results in all membranes.
Conclusions: Preterm PROM without labor is not associated with increased membrane levels of MMP-9 protein, suggesting that its local elevation does not play a role in early membrane rupture.
Keywords: FETAL MEMBRANES; INFLAMMATION; MMP-9; PRETERM BIRTH; PRETERM PROM.