The level of apoptosis is increased during pregnancy. Dying cells emit DNA that remains in blood circulation and is known as cell-free DNA (cfDNA). The concentration of cfDNA can reflect the level of cell death. The present article is the result of studying cfDNA concentration and DNase I activity in the blood plasma of 40 non-pregnant women (control), 40 healthy pregnant women (over 37 weeks) and 40 pregnant women with a diagnosis of intrauterine growth restriction (IUGR). In order to explain the obtained results, a program modeling the change of cfDNA concentration under the influence of different internal and external factors was written. It was reported that, despite the fact that the level of cell death is increased, cfDNA concentration in blood can be decreased due to activation of cfDNA elimination system. A significant increase of DNase I activity has been reported in cases of IUGR. Increase in DNase I activity over a certain threshold indicates presence of pathological processes in the organism. CfDNA circulating in blood cannot be a reliable marker of increased cell death during pregnancy. Thus, assessment of the level of cell death during pregnancy should be done by simultaneous analysis of cfDNA level and DNase I activity.