Oxidative stress is a pathophysiological condition in the body. Pregnancy, mostly because of the mitochondria-rich placenta, is also condition that favors oxidative stress. Oxidative stress during pregnancy peaks by the second trimester of pregnancY. The level of oxidative stress can be monitored by analizing specific biomarkers isolated from biological fluids and tissues. The isoprostanes are prostaglandin like compounds formed in vivo from the free radical-catalyzed peroxidation of essential fatty acids (primarily arachidonic acid. They are considered as markers of lipid peroxidation. 8-isoprostane, as one of their representatives is reliable biomarker of lipid peroxidation and useful in vivo indicator of oxidative stress. The purpose of this study was to examine the value of 8-isoprostane as a marker of oxidative stress during pregnancy.