Hereditary thrombophilias (HT) and undifferentiated connective tissue dysplasia (uCTD) are important causes of female infertility. Moreover, there are signs of their common pathogenesis: a number of proteins, such as PAI-1, play an important role in the pathogenesis of both conditions, as well as in the development of infertility in patients with HT and uCTD Objective — to determine the morphological substrate and molecular mechanisms of impaired pregnancy outcomes in women with uCTD and HT. Subject and methods. A study group included 130 reproductive-aged female patients with primary infertility and a control group consisted of 11 patients (surrogate mothers). An endometrial pipelle biopsy sample was taken from each patient on days 6—8 after ovulation according to the ultrasound findings. The study group patients were divided into subgroups: 1A) infertility and HT (n=91); 1B) infertility, NT, and uCTD (n=19); 1C) infertility and uCTD (n=20).