In this prospective trial, we investigate the effectiveness of maternal Body Roundness Index in predicting the spread of spinal anaesthesia and vasopressor requirement in parturients receiving spinal anaesthesia during the elective caesarean section. We prospectively enrolled 175 parturients. Spinal anaesthesia performed with 10 mg 0.5% hyperbaric bupivacaine at the L3-L4 intervertebral space and the optimal cut-off points of the BRI evaluated as 6.59 by receiver operating characteristic analysis calculating area under the curve. Parturients were divided into two groups with BRI <6.59 and BRI ≥6.59 for analyses. Multivariate logistic regression analysis was used to test for a relationship between variables and maximum sensory block level and vasopressor requirement. BRI was found as an independent risk factor associated with maximum sensory block level (OR = 1.378, 95% CI: 1.125-1.687, p = 0.002). Hypotension and bradycardia events after spinal anaesthesia was not associated with BRI and other variables. The present study indicates that BRI was a practical tool to predict spinal drug distribution in term parturients undergoing caesarean delivery.Impact statementWhat is already known on this subject? Spinal anaesthesia is a commonly used anaesthetic technique for the caesarean section. However, the spinal drug distribution is highly unpredictable. Anthropometric variables may predict the intrathecal drug distribution in parturients. Body Roundness Index (BRI) captures body circumference regarding height to predict body fat percentage, consider the shape of the human body as an ellipse. An ellipsoid body shape might affect the spread of spinal anaesthesia.What do the results of this study add? Our results show that the BRI was as an independent risk factor associated with maximum sensory block level in term parturients undergoing caesarean delivery.What are the implications of these findings for future clinical practice and/or further research? A future study would present the possibility to design a formula for the exact amount of local anaesthetic to be used in spinal anaesthesia with the aid of maternal BRI.