The Effect of the Supine Position on Renal Function in the Near-Term Pregnant Woman12

Abstract
Shifting near-term pregnant women from lying on their sides to lying on their backs resulted in a considerable decrease in the rate of excretion of water and Na. Excretion of K and effective renal plasma flow and glomerular filtration rates usually were not as markedly affected. Renal response to the supine position was not peculiar to pregnancy for similar changes were observed in women with large abdominal neoplasms pelvic in origin. The mechanism by which these changes were produced remains somewhat obscure but appears to involve venous compression rather than ureteral obstruction.