Arterial stiffness is an independent predictor of morbidity and mortality in low and high-risk populations [1]. According to the European Society of Hypertension (ESH) and European Society of Cardiology guidelines, pulse wave velocity, as a direct marker of arterial stiffness, is a valuable parameter in the stratification of cardiovascular risk [2]. Moreover, arterial stiffness is likely to precede hypertension and target organ damage, which has important implications for the early identification of individuals at a high risk of cardiovascular disease [3]. Accordingly, arterial stiffness can reflect vascular health. During pregnancy, an increase in systemic arterial stiffness has been demonstrated to be associated with various obstetric complications, especially preeclampsia, fetal growth restriction, and gestational diabetes [4], [5], [6], [7], [8]. Therefore, assessment of arterial stiffness has been increasingly performed during pregnancy and may have a role as a potential screening tool in pregnancy [4].

Several methods have been used to evaluate arterial stiffness. Of them, carotid‐femoral pulse wave velocity (cfPWV) is the most commonly recommended technique and considered as a reference standard measure [2], [9]. Nevertheless, in the assessment of cfPWV, many patients feel uncomfortable since probes are needed to be applied on both the carotid and femoral arteries, and exposure of the groin area is often unavoidable. Notably, its accuracy is hampered by changes in blood pressure. Moreover, cfPWV is highly operator dependent and sometime is challenging to obtain a good waveform in obese patients. Thus, the use of cfPWV has not been widely practiced. The cardio-ankle vascular index (CAVI) is a novel noninvasive technique to access the arterial stiffness, from the origin of the aorta to the ankle. Importantly, CAVI measurement is independent of blood pressure during the procedure [10], [11], and the reproducibility of measurement is also good [12]. However, during hemodialysis, CAVI may increase, possibly associated with an increase in water removal rate and a decrease in blood pressure, reflecting the contraction of smooth muscle cells in maintaining blood pressure [13]. Because of the advantages, CAVI has been widely used to assess arterial stiffness in patients with cardiovascular diseases and those at risk of developing cardiovascular diseases for early detection and timely treatment of arteriosclerosis and quantitative assessment of disease progression and the effectiveness of treatment. Currently, arterial stiffness assessment has been used in pregnant women to predict adverse outcomes, especially preeclampsia and fetal growth restriction [4], [6], [8], [14]. However, in highly effective assessment during pregnancy, reference ranges of CAVI values for each gestational week should be first established since arterial stiffness is significantly changed during pregnancy [15]. Therefore, we conducted this study primarily aimed to non-invasively establish the arterial stiffness, represented by the cardio-ankle vascular index (CAVI) at various gestational ages among low-risk pregnant women and also to assess mean arterial pressure and heart rate as secondary objectives.