Aim: Oxidative stress is an important factor in pregnancy physiology and embryogenesis. Placental oxidative stress results from deficient trophoblast invasion found to be a cause of a spectrum of disorders including miscarriage, missed miscarriage, and early-and late-onset preeclampsia. Herein, the authors aimed to evaluate serum dynamic thiol/disulphide concentrations in patients with missed abortion and in healthy pregnant women and attempted to determine whether serum thiol/disulphide homeostasis have a role in the pathogenesis of missed abortions. Materials and Methods: This prospective case control study was conducted at the current clinic between January 2015 and January 2016. The demographic characteristics and laboratory parameters of all participants were retrieved prospectively from the each pregnant woman. First-trimester missed abortion was defined as sonographic evidence of an intact gestational sac, no evidence of fetal cardiac activity (after six weeks from last menstrual period), a closed cervical os, and a history of no or minimal bleeding. Patients in the control group were followed up at least until the 20th week of gestation. Thiol/disulphide levels were analyzed with a newly developed method by Erel and Neselioglu. Results: A total of 90 pregnant women were included in this study. The study group consisted of 45 patients with missed abortion, whereas 45 healthy pregnant women were chosen as the control group. All of the patients in the two groups were matched for age, gestational age, and BMI. The authors found significantly increased levels of disulphide (17.1 +/- 4.8 mai vs.11.9 +/- 4.1 mu mol/l) in the sera of the study group compared to the control group (p < 0.001). However serum levels of native thiol and total thiol were statistically insignificant between the two groups. Conclusion: As a conclusion, the authors found a significant increase in serum disulphide levels from the oxidative stress markers in patients with missed abortion. Impaired serum thiol/disulphide homeostasis may he another explanation for the pathogenesis of missed abortion.