This study aims to systematically review the current literature on published studies with data on the clinical significance of endometrial thickness on ultrasound for live birth rate (LBR) after in vitro fertilization (IVF) procedures. A comprehensive systematic review of PubMed, Web of Science, ScienceDirect, Google Scholar, and Open Gray databases and a subsequent hand search of the reference list of included studies was performed. We found 20 eligible studies that evaluated 20 546 patients for endometrial thickness, presented risk factors for decreased endometrial receptivity, and IVF outcomes with fresh and frozen embryo transfer (FET) cycles. The mean age of the patients ranged from 28.86 to 41.03 years. Reported endometrial thickness ranged from 15 mm. The clinical pregnancy rate varied from 9,09% to 61,49% in fresh embryo transfer cycles and from 13,3% to 79,31% in FET cycles. Overall, LBR varied between 4,80% and 48,99% in fresh embryo cycles and between 6.06% and 39,19% in FET cycles. Limitations. Only English-language studies were included; most studies were from the China region; retrospective study design used in most studies; different ET thresholds, which in turn could significantly alter the correlation with pregnancy outcomes; different IVF procedure protocols in fresh or FET cycles. IVF outcomes in patients with impaired endometrial receptivity do not depend only on the condition of the endometrium. Risk factors and endometrial thickness significantly affect LBR in fresh and FET cycles. (www.actabiomedica.it)