Ultrasound estimation of fetal weight is a highly influential factor in antenatal management, guiding both the timing and mode of delivery of a pregnancy. Although substantial research has investigated the most accurate ultrasound formula for calculating estimated fetal weight, current evidence indicates significant error levels. The aim of this systematic review was to identify the most accurate method, whilst identifying sources of inaccuracy in order to facilitate recommendations for future practice. Seven studies met the inclusion criteria and 11 different formulae were assessed; ultrasound calculation of fetal weight was most commonly overestimated. The Hadlock A formula produced the most accurate results, with the lowest levels of random error. Methods incorporating just two measurement parameters were inconsistent, producing large random errors across multiple studies. Key sources of inaccuracy included difficulties obtaining accurate fetal measurements in late gestation; the remainder were operator dependent, including lack of experience and insufficient training and audit. The accuracy of ultrasound estimated fetal weight has improved in the last decade, though a lack of consistency remains evident. National implementation of a rigorous audit programme would likely improve accuracy further, and increase the confidence and clinical value of the method.