Sixty women were examined to evaluate the prooxidant-antioxidant system in those who had the first episode of miscarriage. A control group comprised 30 healthy pregnant women and a study group included 30 women with the first miscarriage in the first trimester. Anamnestic, clinical, laboratory and instrumental data were analyzed. The blood levels of dienic conjugates, malondialdehyde, and catalase were determined by a spectrophotometric method. In the women with the first episode of miscarriage in the first trimester, the values of antioxidant defense and lipid peroxidation were found to be lower than those in the control group. The low blood concentrations of dienic conjugates, malondialdehyde, and catalase were accompanied by termination of early pregnancy. Altered prooxidant-antioxidant homeostasis is a trigger in the initiation of the first episode of miscarriage in women.