- To determine the effect of Ob/Gyn residents' fatigue and training level on the accuracy of their clinical and ultrasonographical estimation of fetal weight (EFW). In this study, clinical and ultrasonographical EFWs were performed by various residents. Actual birth weight, gravidity, parity, gestational age, body mass index, presence or absence of diabetes and hypertensive diseases, presentation and amniotic fluid index were recorded. All EFWs were divided into 3 groups according to the hour they were performed. All residents were divided into 4 groups according to their training level. The accuracy of EFW as compared with actual birth weight was then analyzed according to the shift and to the residents' seniority by using the ANOVA test. Multivariate analysis was performed to evaluate the factors that significantly and independently affected the weight evaluation. Statistically significant differences were found between the clinical EFW and the birth weight among the working shifts for birth weights of 2,500 g and more (p = 0.032 and p = 0.035). For clinical EFW, night shifts were the most inaccurate (9.27, 8.05 and 9.78% of error for day, evening and night shift, respectively; p = 0.03). The accuracy of ultrasonographical EFW was not affected by the residents' fatigue level. The residents' training level did not alter the accuracy of either clinical or sonographical EFW. The accuracy of clinical EFW was affected independently by the work shift (p = 0.01), whereas no factor was found to independently effect the accuracy of ultrasonographic EFW. Ob/Gyn residents' fatigue affects the accuracy of clinical but not ultrasonographical EFWs. Residents' training level does not alter either the clinical or sonographical EFW.