Pulse wave analysis in normal pregnancy: a prospective longitudinal study

Abstract

Background: Outside pregnancy, arterial pulse wave analysis provides valuable information in hypertension and vascular disease. Studies in pregnancy using this technique show that vascular stiffness is raised in women with established pre-eclampsia. We aimed to establish normal ranges for parameters of pulse wave analysis in normal pregnancy and to compare different ethnic groups.

Methodology/principal findings: This prospective study was conducted at The Homerton University Hospital, London between January 2006 and March 2007. Using applanation tonometry, the radial artery pulse waveform was recorded and the aortic waveform derived. Augmentation pressure (AP) and Augmentation Index at heart rate 75/min (AIx-75), measures of arterial stiffness, were calculated. We recruited 665 women with singleton pregnancies. Women who developed pre-eclampsia (n = 24, 3.6%) or gestational hypertension (n = 36, 5.4%) were excluded. We also excluded 47 women with other pregnancy complications or incomplete follow-up, leaving 541 healthy normotensive pregnant women for subsequent analysis. In the overall group of 541 women, there were no significant changes in AP or AIx-75 as pregnancy progressed. In 45 women followed longitudinally, AP and AIx-75 fell significantly from the first to the second trimester, then rose again in the third (P<0.001). The two main ethnic groups represented were Caucasian (n = 229) and Afrocaribbean (n = 216). There were no significant differences in AP or AIx-75 in any trimester between these two ethnic groups.

Conclusions: This study is the largest to date of pulse wave analysis in normal pregnancy, the first to report on a subset of women studied longitudinally, and the first to investigate the effect of ethnicity. These data provide the foundation for further investigation into the potential role of this technique in vascular disorders in pregnancy.

Figure 1. Recruitment and progression of participants through the trial.

Figure 2. The central (aortic) pulse waveform, represented schematically.

A. Typical ascending aortic pulse waveform, showing two systolic peaks (P1 and P2). Augmentation index (AIx) is calculated as the difference between P2 and P1, expressed as percentage of pulse pressure. In hypertensive disorders arterial wall stiffness is increased; the arterial pulse wave travels faster, so the reflected wave reaches the advancing wave in systole, resulting in greater augmentation of the systolic peak. P1 = the first inflection point; P2 = the second inflection point.

Figure 3. Pulse wave analysis parameters according to gestation.

Scatter plots of (a) augmentation pressure (AP), and (b) augmentation index at heart rate of 75/min (AIx-75) according to the gestational age in days (n = 541). The 5^th and 95^th centiles are shown. Only one measurement from each woman is included.

Figure 4. Monthly changes in augmentation index at heart rate of 75/min, central and peripheral blood pressure.

Monthly [10⁺⁰–13⁺⁶ weeks (n = 145), 14⁺⁰–17⁺⁶ weeks (n = 56 ), 18⁺⁰–21⁺⁶ weeks (n = 55 ), 22⁺⁰–25⁺⁶ weeks (n = 104), 26⁺⁰–29⁺⁶ weeks (n = 86), 30⁺⁰–33⁺⁶ weeks (n = 57 ) and 34⁺⁰–37⁺⁶ weeks of gestation (n = 38)] changes throughout pregnancy in: (a) augmentation index at heart rate 75 beats per minute (AIx-75), and (b) brachial and aortic blood pressures. Values represent mean values and error bars represent standard errors. Only one measurement from each woman is included. BP = blood pressure.

Figure 5. Longitudinal changes in pulse wave analysis parameters.

Longitudinal data for the 45 women who had measurements taken at 12⁺⁰–12⁺⁶ weeks, 23⁺⁰–23⁺⁶ weeks, and 32⁺⁰–32⁺⁶ weeks of gestation: (a) augmentation pressure (AP), and (b) augmentation index at heart rate 75 beats per minute (AIx-75).