This study aimed to evaluate if endometrial length (EL) affects the likelihood of a positive pregnancy test in individuals who had in vitro fertilization/intra cytoplasmic sperm injection (IVF/ICSI). Between December 2020 and June 2021, 100 women from those referred to the High Institute for Infertility Diagnosis and Assisted Reproductive Technologies, Al-Nahrain University, for IVF/ICSI were selected. These women were 20–40 years old with primary type sub-fertility and met the inclusion criteria. Controlled ovarian hyperstimulation (antagonist protocol), followed by transvaginal sonography (TVS), was used to measure the endometrial length (EL) from the internal ostium to the fundus on the day of ovum collection. Afterwards, the association between endometrial length and the outcome was examined. The data were analyzed using the Statistical Package for Social Sciences (SPSS). The data show an important link between EL and treatment success. Endometrial length of ≥39 mm was considered a good cut-off point for IVF/ICSI pregnancy rates with a sensitivity of 75%, a specificity of 68%, a positive predictive value of 57%, and a negative predictive value of 83, and area under the curve of 0.81. An endometrial length of 39 mm can be used as an appropriate cut-off point in IVF/ICSI to predict a greater pregnancy rate. Vaginal sonography could be used in the ART cycle to measure the endometrial length and thickness and to determine endometrial receptiveness.