Normal pregnancy is associated with enhanced endothelium-dependent flow-mediated vasodilation.

Normal pregnancy is characterized by reduced systemic vascular resistance, which may be mediated by nitric oxide (NO). We compared endothelial vasomotor function in 71 normal pregnant women (13 in first, 29 in middle, and 29 in last trimester) to 37 healthy age-matched controls. With external ultrasound, brachial artery diameter was measured at rest, during reactive hyperemia [with increased flow causing endothelium-dependent dilation (FMD)], and after sublingual nitroglycerin (causing endothelium-independent dilation). Compared with controls, resting flow and brachial artery diameter were significantly higher during the middle and last trimesters. Reactive hyperemia was reduced in all pregnant groups. FMD increased from the first trimester (by 26%), reaching the highest value in the last trimester (to 47% above nonpregnant values). FMD was significantly correlated to pregnancy status (nonpregnant or pregnant) and to vessel size. Nitroglycerin-induced dilation was similar in pregnant and nonpregnant women. A longitudinal study of eight women evaluated in the first, middle, and last trimesters confirmed an increase in FMD throughout pregnancy. The study supports the idea that basal and stimulated NO activity is enhanced in normal pregnancy and may contribute to the decrease in peripheral resistance.