[Sodium restriction during pregnancy: an outdated advice]

Abstract

Even in an early phase of pregnancy marked haemodynamic changes occur, including a fall in vascular resistance and blood pressure and a rise in cardiac output. To compensate for the increased intravascular capacity the kidney retains more sodium and water. Apparently, the set point of sodium homeostasis shifts to a higher level at the expense of an expansion of extracellular volume. Studies during the normal menstrual cycle have shown that these changes, albeit smaller, also occur during the luteal phase. These fluctuations with the menstrual cycle are less apparent if salt intake is low, suggesting that a high salt intake is needed to facilitate the process of sodium retention. In pregnancies complicated by hypertension and/or pre-eclampsia body fluid volumes are low with an enhanced tendency to retain sodium after a volume challenge. These data, together with the lack of an apparent benefit of sodium restriction, suggest that the practice of prescribing a low-salt diet to hypertensive pregnant women should be abandoned.