Muscle sympathetic nerve activity peaks in the first trimester in healthy pregnancy: a longitudinal case study

Abstract

Objective and methods: Muscle sympathetic nerve activity and baroreflex sensitivity were examined at rest before, during (weeks 6, 11, 17, 22, 25, 33 and 36) and after a normotensive pregnancy.

Results: Muscle sympathetic nerve activity is elevated during pregnancy with a large peak in the first trimester (D17 bursts/min) and a secondary peak in the third trimester (D11 bursts/min). Cardiac baroreflex sensitivity peaked in the first trimester (10 vs. 6 ms/mmHg prepregnancy), whereas sympathetic baroreflex sensitivity was greater throughout.

Interpretation: The increase in sympathetic outflow early in pregnancy cannot be explained by a reduction in baroreflex sensitivity, while the secondary increase in burst frequency in the third trimester may, in part, be explained by the elevated heart rate.