ABSTRACT
The spread of spinal anesthesia in parturients with singleton and those with twin pregnancies was compared in relation with progesterone levels in plasma and CSF. Twenty unpremedicated parturients with uncomplicated pregnancy scheduled for cesarean section were allocated to two groups: Group I = 10 singleton mothers and 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. A statistically significant difference in the cephalad spread of spinal anesthesia [group I up to T5 and group II up to T3] was found. The mechanisms of higher cephalad spread of spinal anesthesia in the twin group may be 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