Brachial and femoral blood pressures during the prenatal period.

In 202 young primigravidas, right-sided brachial and femoral arterial pressures were recorded in both supine and left lateral positions during prenatal visits in the second and third trimesters. Roll-over tests were performed in 78 of these. Position-related falls predominantly in femoral artery pressure--indicative of aortic compression-were demonstrable earlier and with greater frequency than falls predominantly in brachial artery pressure-indicative of caval compression. While the sequelae of caval compression were perceived by the gravida, those of aortic compression were not. Therefore, education to the risks of the supine position should start early in pregnancy. There was no relationship between decreases in blood pressures and subsequent development of pre-eclampsia. Roll-over tests were positive in 45 gravidas (58%) and pre-eclampsia developed in 15 (33%). Roll-over tests were negative in 33 gravidas (42%) and pre-eclampsia developed in two (6%). This difference was significant at the 0.02 level.