Effect of left-lateral position on maternal hemodynamics during ritodrine treatment in comparison with supine position.

Pregnant women are generally recommended to rest in the left-lateral position (l-lat.) to avoid caval compression. We studied the influence of postural change from the supine position (sup.) to the l-lat. on maternal hemodynamics and tocolysis. The cardiac output (CO) was measured by impedance cardiography, while the pulsatility index of the uterine artery (PIUtA) was determined by the pulsed Doppler method. When the maternal posture was changed from sup. to l-lat, the following results were obtained. (1) The frequency of uterine contractions (UC) (preterm labor = 92) was significantly reduced (p less than 0.01). (2) The resting uterine tonus (n = 5) was also significantly decreased (p less than 0.05). (3) In the cases showing a decrease in the frequency of UC, the CO value was significantly increased (p less than 0.01), whereas PIUtA was significantly decreased (p less than 0.01). It is concluded that the postural change from sup. to l-lat. resulted in a decrease in the frequency of UC and the resting uterine tonus and at the same time an increase in the CO and decrease in the vascular resistance of the uterine artery.