Spinal fluid(CSF) was analyzed in ten pregnant women at term undergoing C-section with spinal anesthesia and in ten non-pregnant women undergoing gynecological operation with spinal anesthesia. The acid-base status, protein and sugar levels in the CSF of the CSF are summarized in Table-2 and Table-3. The pH was slightly higher in the pregnant group compared to that of the non-pregnant controls. The bicarbonate level and the total CO2 content were significantly lower in the pregnant group compared to non-pregnant controls. The protein and sugar level were lower in the pregnant group compared to non-pregnant controls. Acid base changes can markedly affect dissociation of the local anesthetics. More free base will be available for transfer across lipid barriers in a relatively more alkalotic medium which was found in spinal fluid of pregnant women. In addition, lower bicarbonate levels may also affect dissociation of local anesthetic and activity by changing the buffering capacity. In conclusion, our results show that pregnancy induces significant changes in the acid base balance of the spinal fluid. These changes may contribute to the facilitated spread of local anesthetics in both the epidural and subarachnoid spaces.