Abstract We have compared the spread of spinal anaesthesia in parturients with singleton and those with twin pregnancies, in relation with progesterone levels in plasma and CSF. Twenty unpremedicated parturicnts with uncomplicated pregnancy scheduled for caesarean section were allocated to two groups; group 1= 10 singleton mothers, group II = 10 with twin pregnancy. Both groups received spinal anesthesia with hyperbaric bupivacaine 10 mg (2 ml of 0.5%). Progesterone levels in CSF and plasma were estimated just before the procedure. We found a statistically significant difference in the cephalad spread of spinal anaesthesia (group 1 up to TS and group 11 up to T3). The mechanisms of higher cephalad spread of spinal anaesthesia in the twin group i-nay he a decrease in CSF fluid volume due to shunting of blood from the compressed inferior vena cava to extradural venous plexus and increased nerve sensitivity to the local anesthetic because of increased concentrations of progesterone. The twin pregnancy group had heavier placentae and greater daily production of progesterone. Key Wsprds: Progesterone - Spinal anesthesia - Caesarean section

Introduction It was observed that parturients with twin pregnancy had a rapid onset and higher cephalad spread of spinal anaesthesia during caesarean section compared with those with a singleton pregnancy [I]. Compression of the inferior vena cava secondary to the larger gravid uterus has been shown to he an important factor in higher cephalad spread of spinal anaesthesia [2]. The sensitivity of nerve fibres to local anaesthetic agents during pregnancy has