Factors influencing aortocaval compression in late pregnancy.

The circulatory effects of postural change in late pregnancy were investigated in 20 healthy pregnant women. Maximum stroke volume (93.2 +/- 11.9 ml) was recorded with the subject in the left lateral position and was significantly (p less than 0.001) reduced in the supine, right lateral, and lithotomy positions, but was largely unchanged in the standing motionless position (89.9 +/- 12.6 ml). Diastolic, systolic, and mean arterial blood pressures and total peripheral vascular resistance were significantly (p less than 0.001) increased in the supine, right lateral, lithotomy, and upright motionless positions when compared to the same variables in the left lateral position. The following factors were found to be significantly correlated to the hemodynamic response to the supine recumbent position: maternal age (p less than 0.05), the position of the fetus in the uterus (p less than 0.05), and systolic (p less than 0.001) and diastolic (p less than 0.001) blood pressures measured with the subject in the left lateral position. The implications of the present findings for modern obstetric delivery care and the etiology of the supine hypotensive syndrome are discussed.