Spinal needles with different diameters can be used to prevent side effects in patients undergoing spinal anaesthesia. However, the velocity of local anaesthetic changes through the spinal needle depending on the diameter of it. Local anaesthetic injection velocity has been reported to be associated with the spinal block level. We aimed to compare spinal needles of different diameters with the same local anaesthetic volumetric flow rate in terms of spinal blockade and hemodynamics in obstetric patients. Eighty-four patients received spinal anaesthesia by either a 25G needle or 29G with the same volumetric flow rate. Block levels, adverse effects, ephedrine given and a success rate of spinal anaesthesia were significantly higher in 25G than in 29G (p<.05). Athough the use of 29G was associated with a low level of block, a sufficient block level was generated for caesarean section. Furthermore, in spite of the technical difficulty, use of 29G was accompanied by a decreased incidence of maternal hypotension, bradycardia and a lowered ephedrine administration.Impact statementLocal spinal anaesthetic injections at faster flows cause turbulent flow leading to lower anaesthesia concentrations.The control of spinal anaesthesia levels has some difficulties due to anatomical repositioning, especially in pregnant patients.Also, it can cause frequent hemodynamic complications including hypotension and bradycardia, complications that may also have inadvertent effects on foetus.In this study, we showed that smaller diameter spinal needles provided safer spinal anaesthesia levels and a lower incidence of hemodynamic complications.