Preeclampsia (PE), one of the most serious complications of pregnancy, is characterized by endothelial dysfunction and hypertension. The pathophysiology of the disease is still unknown; however, evidence suggests that placental and maternal oxidative stress promote the disease process. Several studies have assessed levels of oxidative stress during pregnancy, but after diagnosis of PE. However, few studies have examined oxidative stress before PE diagnosis. Thus, the present work was aimed to gain further insight into the role of oxidative stress prior to diagnosis of PE (i.e. 12-20 weeks of gestation) and to further understand and predict PE incidence. Blood levels of superoxide (O2-) and erythrocyte antioxidants such as superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH) and oxidized glutathione (GSSG) levels were measured in 23 preeclamptic pregnant women and 91 women with normal pregnancies. We further used logistic regression of O2- and each antioxidant level as the main predictor variable for PE risk. CAT activity, GSH, and Total glutathione (TGSH) were significantly lower with All PE pregnant groups, whereas O2- levels were modestly, but significantly, higher in women with mild PE. Logistic regression analysis suggests increased CAT activity in pregnant women is associated with a decreased odds of being preeclamptic. CAT is the only antioxidant as shown in our study to be related to the severity of the disease and may be a promising predictor for PE. Further studies are warranted to investigate the use of CAT as a novel therapeutic for PE. Published by Elsevier B.V.