Background: The most frequent gynecological procedure, caesarean section (CS), is linked to the advantages and disadvantages of elective repeat caesarean (ERC) and vaginal birth after cesarean (VBAC). Recent research has revealed that VBAC is less safe than previously thought due to an elevated risk of problems that may be associated to lower uterine segment (LUS) thickness. The LUS has been measured with ultrasound (US) using a variety of methods, including transabdominal (TA) and transvaginal procedures. The LUS thickness may be measured more precisely using 3D US than 2D US.Objective: The aim of the current study was to use 2D and 3D ultrasonography across the abdomen following previous CS to gauge the lower uterine wall's thickness before childbirth. Patients and methods: A cross sectional study was carried out at the Obstetrics and Gynecology Department of the Faculty of Medicine, Al-Azhar University of Boys, from November 2021 to November 2022. The study included pregnant women, aged more than 18 years old, with gestational age between 37 and 39 weeks, with past history of one CS. Multiparous women, pregnant women with polyhydramnios or placenta previa were excluded. All participants were subjected to full history taking and thorough complete clinical examination. Ultrasound exams were carried out using a device with a 4-8 MHz transducer for 2D and 3D volume scanning. Results: The best cutoff value for 2D US was 3.91 mm with an AUC of 0.742, and this resulted in significant diagnostic accuracy with sensitivity 82.5%, specificity 69.3%, PPV 77.8%, and NPV 75%. The mean LUS thickness by 2D transabdominal US was 6.74 1.52 mm, while by 3D transabdominal US it was 5.86 1.43 mm. Conclusion: Thickness of the lower portion of the uterine wall may be precisely measured before delivery using both 2D and 3D ultrasonography, with 3D ultrasound having a better degree of accuracy. Obstetricians can still use 2D ultrasound in locations without 3D technology.