Whether brachial artery FMD (flow-mediated dilation) is altered in pregnancy by 28–35 weeks compared with non-pregnant women remains controversial. The controversy may be due to limitations of previous studies that include failing to: (i) test non-pregnant controls in the mid-late luteal phase, (ii) account for effects of pregnancy on the dilatory shear stimulus, (iii) account for physical activity or (iv) control for inter-individual variation in the time to peak FMD. In the present study, brachial artery FMD was measured in 17 active and eight sedentary pregnant women (34.1±1.6 weeks of gestation), and in 19 active and 11 sedentary non-pregnant women (mid-late luteal phase). Decreased vascular tone secondary to increased shear stress contributes minimally to pregnancy-induced increases in baseline brachial artery diameter, as shear stress removal during distal cuff inflation in pregnant women did not reduce diameter to baseline levels observed in non-pregnant controls. Neither the shear stimulus nor the percentage FMD was affected by pregnancy or regular exercise. Continuous diameter measurements are required to control for delayed peak dilation during pregnancy (57±15 compared with 46±15 s; P=0.012), as post-release diameter measured at 60 or 55–65 s post-release underestimated FMD to a greater extent in non-pregnant than in pregnant women.

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