The article presents the analysis of the massometric parameters of the fetoplacental complex (weight of the placenta of full-term newborns, placental-fetal coefficient (PPC), linear mass of the umbilical cord (LMU). Indicators that alarm the neonatologist doctor as possible markers of perinatal losses are: a decrease in the placenta mass, an increase in PPC, high LMU (a consequence of ascending bacterial infection (funiculitis) and the development of circulatory umbilical edema in acute right ventricular failure, for example, in viral atrial myocarditis). A histological study of newborn children of the main and control group was carried out to identify the main types of histological structure of the placenta: normal structure, ascending infection of the placenta, hematogenous infection of the placenta, chronic placental insufficiency, acute placental insufficiency. revealed a different frequency of occurrence of these conditions in patients of the main and control groups. The main causes of perinatal losses are analyzed. It is determined that more than half of cases of perinatal fetal death is infectious pathology: viral, bacterial and mixed viral-bacterial. About a quarter of cases of perinatal death is caused by acute heart failure with placental abruption and a complex of cardiovascular and respiratory disorders in premature infants. In 18% of cases, congenital malformations of the fetus lead to perinatal death. CRF causes perinatal fetal death in approximately 10% of cases. (For citation: Ivanova LA, Titkova EV. Peculiarities of the construction of the placentary complex and the main causes of perinatal losses. Pediatrician (St. Petersburg). 2018;9(1):5-10. doi: 10.17816/PED915-10).