<scp>ISUOG</scp> Consensus Statement on maternal hemodynamic assessment in hypertensive disorders of pregnancy and fetal growth restriction

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice, and high-quality teaching and research, related to diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has the remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach, from experts, for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practice at the time at which they are issued. Although ISUOG has made every effort to ensure that Guidelines and Consensus Statements are accurate when issued, neither the Society nor any of its employees or members accepts any liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. The ISUOG CSC documents are not intended to establish a legal standard of care because interpretation of the evidence that underpins them may be influenced by individual circumstances, local protocol and available resources. Approved Guidelines and Consensus Statements can be distributed freely with the permission of ISUOG ([email protected]). Pregnancy presents a unique cardiovascular challenge. Profound maternal hemodynamic adjustments result from a complex interplay between the maternal cardiovascular system and uteroplacental perfusion, which permits fetal development while maintaining healthy maternal homeostasis1-5. Failure to meet this challenge can lead to maternal hypertensive complications (hypertensive disorders of pregnancy (HDP)) and/or fetal growth disorders (fetal growth restriction (FGR))6-9. Monitoring and management of HDP and FGR has been based largely on maternal blood pressure (BP) monitoring and fetal growth assessment10. Promising research offers the prospect of a less reactive and more proactive approach. Maladaptation to the requirements of pregnancy can be detected in a preclinical phase of HDP and FGR by maternal hemodynamic assessment, offering opportunities for targeted hemodynamic interventions11-15. Pregnancy also serves as a stress test for future cardiovascular health, especially if superimposed upon subclinical cardiometabolic or cardiovascular vulnerabilities11, 16-19. This Consensus Statement provides an update on the role of maternal hemodynamic assessment in HDP and FGR. A proposal for this Consensus Statement was submitted to and evaluated by the ISUOG CSC. The authors of this Consensus are members of the International Working Group on Maternal Hemodynamics (https://maternalhemodynamics.com/) and were involved in both the development and the writing stages. Members of the International Working Group on Maternal Hemodynamics who were not involved in the writing of this Consensus were invited to review the document (reviewing group) and those who responded are acknowledged. Stakeholders were not included in the writing process. This process was not intended to represent a systematic review. The preselected topics were divided among the authors, who worked in pairs and performed a literature search. T.S. collated the document and proposed the key points. The final document and key points were revised by all authors. Several meetings were organized to discuss any points on which there was not initial consensus, until complete agreement was reached. The document was then finalized after comments from the reviewing group, the ISUOG CSC and the ISUOG Board of Trustees. The authors of this Consensus Statement are experts in the field of maternal hemodynamics and have expressed their opinion based on the available literature and evidence. Any clinician applying this Consensus is expected to use their independent medical judgement in the context of the individual clinical circumstances to determine patient care. Traditionally, peripheral BP is measured by auscultation using an arm cuff connected to a manometer. Increasingly, automated oscillometric devices, validated for pregnancy, are becoming the recommended standard20, 21. Further developments have allowed additional analysis of the arterial waveform for estimation of central BP and arterial function. Markers of arterial stiffness and compliance, such as pulsed-wave velocity and the augmentation index (AIx)22, 23, help to understand the pathophysiology behind HDP and FGR, predict cardiovascular complications, and evaluate and direct prevention and treatment24-26. Assessment of central hemodynamic factors that determine BP (cardiac output (CO, in L/min) and systemic vascular resistance (SVR, in dyne.s/cm5)) is increasingly accessible using easily operable devices27. Considering the pivotal role of central hemodynamic functioning, this Consensus Statement focuses primarily on CO assessment. CO is the product of stroke volume (SV) and heart rate (HR) (CO = SV × HR). Accuracy of its evaluation is improved by averaging measurements over several heartbeats3-5, to compensate for respiratory variations. After 20 gestational weeks, CO is best evaluated with the woman in a left lateral position, to minimize caval and aortic compression by the gravid uterus28, 29. The heart can rapidly modulate CO in order to meet the demands of pregnancy, with a wide range of normality (4–20 L/min) depending on activity level, age, fitness, body size, gestational age and metabolic rate. While trimester-specific reference ranges exist, device-specific normalization, that takes into account maternal age and posture, does not. Indexing for actual or prepregnancy body surface area or height may be of additional value when comparing measurements between individuals27, 30-32. Individual or separate CO measurements can be of value for instant hemodynamic assessment, while repeated or continuous measurements are appropriate for trend analysis. With knowledge of CO and BP, SVR can be calculated ((SVR = 80 × (MAP − RAP)/CO) in dyne.s/cm5), where MAP represents mean arterial pressure and RAP is right atrial pressure. RAP (or central venous pressure) is usually low in pregnancy (0–5 mmHg) and therefore is usually omitted from the calculation33, 34. Arterial function can also be evaluated by Doppler assessment of peripheral vessels, for example the uterine and/or opthalmic arteries. CO is determined most accurately by invasive measurements using thermodilution or indicator (lithium) dilution, or by cardiac magnetic resonance imaging (MRI). The former require insertion of intracardiac, central venous and/or arterial catheters (e.g. pulmonary artery catheters), limiting their indication to critically ill pregnant women in an intensive care unit setting33, 34 . Cardiac MRI is non-invasive, but its limited availability and high cost restrict its use in an obstetric context28, 35. Transthoracic echocardiography permits non-invasive assessment of CO by measuring the left ventricular outflow tract diameter and pulsed-wave Doppler outflow signal along with HR. It has been validated against invasive measurements in severely ill pregnant women and can be considered an alternative reference technique36, 37. Transthoracic echocardiography enables evaluation of systolic and/or diastolic function (assessing ejection fraction using two-dimensional and/or M-mode imaging, strain and strain rate using speckle tracking, tricuspid annular plane systolic excursion (TAPSE), and mitral inflow using pulse-wave and tissue Doppler imaging) and preload assessment (atrial size and inferior vena cava size and collapsibility)38-40. Another means of assessing CO is with a non-invasive mobile device, using a continuous-wave Doppler transducer placed in the suprasternal notch40. This technique is limited by assumptions regarding the left ventricular outflow tract diameter and acoustic guidance for probe orientation. However, by including more heartbeats in the calculation, the accuracy is enhanced. An inert gas rebreathing technique can be used to calculate CO based on Fick's principle41. A blood-soluble and an insoluble gas are delivered though a closed breathing assembly and relative levels over a few respiratory cycles are measured by a gas analyzer in the mouthpiece. 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