The article describes the case of prenatal diagnosis of Down’s syndrome in a 17 weeks of gestation fetus in a 39-year-old pregnant woman with the first detected giant necrotic uterine myoma and a tendency to hypercoagulable against the background of the heterozygous carriage of the Leyden mutation. At 20 weeks of gestation, due to the inability to proliferate through the natural birth canal, extirpation of the uterus with the fetus (without appendages) was carried out along the Rhine-Poros. At autopsy the diagnosis was confirmed. Timely medical and prophylactic measures allowed to avoid the development of thrombogenic complications. The article discusses the complications of the course of pregnancy with uterine myomas, as well as the features of the echographic pattern of degenerative changes in the myomatous nodes, indications for an operative delivery for uterine myomas, and the frequency of carriage of the Leiden mutation in the population. Key words: uterine myoma, Leyden mutation, ultrasound diagnosis,invasive prenatal diagnosis, Down’s syndrome.