Objective — to calculate frequency of vaginal and uterine infection in patients with spontaneous preterm delivery. Material and methods. A comparative study included 102 pregnant women aging from 22 to 45 y.o. that were admitted to «Family planning and human reproduction center» affiliated to Moscow city Department of Health for delivery in the period from 2016 to 2017. 90 of the women mentioned above delivered at 22—36.6 weeks of pregnacy (spontaneous preterm delivery group), another 12 patients with 38—41 week pregnancy that made delivery at term formed a comparison group. Complaints, anamnestic data, physical and ginaecological anamnesis, clinical-laboratory examination, ultrasonical examination of pelvic organs and histopathological examination of placentae were collected from the patients. 24 randomly chosen women from the group of preterm delivery were additionally examined concerning vaginal discharge (right after the prelabor rupture of membranes) and uterine discharge (intraoperative during the C-section) for performing real-time PCR with «Florozenoz — bacterial vaginosis» and «Florozenoz mycoplasmae» tests. These tests were used to calculate the percentage of lactobacillus in bacterial burden per 10 000 cells and to detect opportunistic microorganisms, cytomegalovirus and herpes simplex viruses 1 and 2 (CMV, HSV-1, HSV-2). Statistical processing of data was provided using the Statistica 10.0 («Statsoft Inc.», USA) software. The methods used for calculating of non-parametric data are U criterion of Mann—Witney and Spearman correlation analysis (test significance p<0.05). Results. Recieved data from real-time PCR of vaginal discharge showed that 75% of women with preterm delivery (average prolonged rupture of membranes time was 24.07 hours) have had vaginal dysbiosis and 41.6% have had bacterial vaginosis. In the same time, all women with spontaneous delivery had normal vaginal microbiota and only in 25% of cases uterine dysbiosis. Simultaneously in vaginal microbiota of women with preterm delivery, there was a 30% increase (in vagina) and 50% increase (in uterine cavity) of opportunistic microorganisms in contrast to comparison group. Pathology examinations of placentae (coupled with PCR of women’s genital discharge) showed significance of hematogenic (transplacental) and ascending routes of transmission in the development of preterm delivery. Conclusions. Mentioned above information suggests that in order to prevent a complication of pregnancy such as preterm labor it’s important to examine condition of microflora for early detection and treatment of vaginosis and uterine dysbiosis. Simultaneously, our study is consistent with literature data about subclinical intrauterine infection in genesis of preterm labor.