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There is evidence of impaired placental development in intrauterine growth restriction (IUGR). Matrix metalloproteinases (MMPs) are extracellular matrix-degrading enzymes that are released by placental cells during tissue remodeling processes. We hypothesized 1) that release of MMP-2 and -9 is decreased and/or release of tissue inhibitors of metalloproteinases (TIMPs) is increased from placental explants in pregnancies complicated by IUGR and 2) that oxygen levels affect such release.Placental villous explants from normal (n = 7) and IUGR (n = 7) pregnancies were cultured at high (20%) and low (3%) oxygen levels for 24 hours. Supernatants were analyzed for MMP-2 and MMP-9 by zymography and for TIMP-1 and -2 by western blot analysis.: At 20% oxygen there was significantly reduced MMP-2 (P.05) and TIMP-1 (P.01) release and a trend for decreased MMP-9 release (P = .07) in explants from IUGR pregnancies compared with normal pregnancies; however, there were no differences at 3% oxygen. TIMP-2 was below detectable levels in all samples. Although MMP-2 and TIMP-1 release was significantly reduced at 3% compared with 20% oxygen in explants from both normal (P.001; P.05) and IUGR (P.05) pregnancies, MMP-2 release changed less in IUGR compared with normal explant cultures. There were no significant effects of oxygen on MMP-9 release.Placental explants from IUGR pregnancies demonstrated reduced MMP-2, MMP-9, and TIMP-1 release compared with explants from normal pregnancies at high (20%) but not low (3%) oxygen.