Decreased intervillous and unchanged myometrial blood flow in supine recumbency.

The supine position in late pregnancy is associated with many hemodynamic changes caused by compression of the inferior vena cava and a resulting fall in cardiac output. To investigate the effect of this position on uteroplacental blood flow, 22 women with normal (N = 12) or hypertensive (N = 10) pregnancy were investigated using the intravenous 133Xe washout method, in both the supine and left-tilted (45-degree) lateral positions. The intervillous blood flow (113 +/- 48 ml/min/dl) was lower in the supine position than in the left-tilted position (141 +/- 48 ml/min/dl) (P less than 0.01), while the myometrial blood flow was similar in both (9.0 +/- 3.3 ml/min/100 g in supine and 8.7 +/- 2.7 ml/min/100 g in left-tilted position). The results suggest that the autoregulation system for uteroplacental circulation is operative only in the nonplacental component of the pregnant uterus.