The clinical and hemostasiological features of the course of pregnancy were evaluated and the level of annexin V, placental anticoagulant protein, was studied in 113 women with threatened miscarriage of different genesis (antiphospholipid syndrome, hyperandrogenism, and persistent virus infection). A control group comprised 40 healthy pregnant women. The characteristic obstetric complications (anemia, gestosis, and fetoplacental insufficiency) accompanied by higher titers of anti-annexin V antibodies were established in antiphospholipid syndrome; a number of obstetric complications (early toxicosis, preeclampsia, placental insufficiency, isthmicocervical failure) were also revealed in persistent virus infection and hyperandrogenism; however, no statistically significant changes in annexin V content were found. In pregnant women with antiphospholipid syndrome and persistent virus infection, the development of obstetric complications was accompanied by impairments in the hemostatic system.