Background/Objectives: Non-receptive endometrium is associated with recurrent implantation failure, which leads to a decrease in the frequency of pregnancy during IVF; therefore, new treatment methods such as the use of Platelet-Rich Plasma (PRP) are gaining popularity in the treatment of infertility in women with repeated unsuccessful IVF attempts. Methods: A total of 38 women were included in this study, with the main complaint being the inability to conceive or maintain pregnancy. Medical examination, laboratory tests, ultrasound of the pelvic organs and hysteroscopy were performed. After that, whole blood was taken to prepare an autologous PRP; then, the PRP was inserted into the uterine using an intrauterine catheter in the first phase of the menstrual cycle (1–7 procedures). The primary outcome of this study was an increase in endometrial thickness and improvement of the receptive endometrial layer. The secondary outcome was pregnancy rate. This was a single-center prospective interventional clinical study. Results: Statistical analysis of changes in endometrial thickness after PRP therapy showed that endometrial thickness indicators after treatment significantly exceeded the values before the intervention. This may be evidence of the effectiveness of PRP therapy for thin endometrium. When analyzing pregnancy status, it was noted that after receiving PRP, more than half (56% of cases) became pregnant and the majority of them successfully gave birth. Conclusions: Based on the results of our study, we can conclude that intrauterine injection of PRP may be a new therapeutic approach in the treatment of thin endometrium and associated infertility. The use of PRP demonstrated effectiveness in increasing the thickness of the endometrium, regardless of pregnancy, while the secondary indicator was the frequency of successful pregnancies among the participants.