Physiology of veins in pregnancy

Abstract

One largely unpredictable disaster in pregnancy is venous thrombosis and pulmonary embolism; this is the main cause of maternal mortality in the United Kingdom today, and basic research into the pathophysiology of this disorder is welcome. Two papers in this month's issue study the changes in diameter and blood flow in the veins of the lower limb in pregnancy. Colette Sparey and her colleagues (pages 557–562) measured the diameters of several veins in the leg in thirty women using colour flow duplex Doppler ultrasound, and found that the diameter of the long saphenous vein increased progressively in pregnancy until about 34 weeks of gestation, decreasing towards term, and on the left side, into the puerperium. Similar although less marked changes were seen in the deep veins of the thigh, at the knee and in the calf. No venous reflux was found in any of the women. Alexandra Biichtemann and her colleagues (pages 563–569) go further, by measuring both venous diameter and blood flow in the veins of the lower limb in fifteen pregnant women before and after the application of graduated compression stockings. The diameter of the superficial femoral vein is similar in the two studies, and Biichtemann and colleagues confirm that it increases throughout pregnancy. The authors show also that with graduated compression stockings the diameter of the superfkial femoral vein decreased, the volume of blood expelled from the leg on dorsiflexion increased, the time for refilling of the veins decreased and that the velocity of blood flow in the legs increased. Our intuition leads us to expect the results of these studies, yet they are among the first to investigate formally the function of veins in the lower limb throughout pregnancy and in the puerperium. Our greater understanding of the basic science of venous physiology and pathophysiology will help us to prevent the dreaded complications of venous thrombosis and pulmonary embolism associated with pregnancy.