Reference ranges of fetal cardiac biometric measurements by HeartAssist? in the Korean population: a multicentre prospective study

To provide reference ranges for fetal cardiac parameters by using HeartAssist™, an automated system for measuring such parameters, in 17 large referral centres in South Korea. This prospective study included normal singleton fetuses between 16.0 and 36.6 weeks of gestational age (GA) from October 2022 to February 2023. Video clips of the fetal hearts were collected, and a total of 34 parameters were measured in six cardiac views. In the four chamber view, we measured cardiac axis; thoracic area and circumference; heart area and circumference; atrial widths and areas; ventricular widths, lengths, and areas; and annular diameters of the tricuspid and mitral valves. In the outflow tract view, annular diameters of the aortic and pulmonary valves when open and closed and the diameter of the ascending aorta were measured. In the three vessel view, diameters of the pulmonary artery, aorta, superior vena cava, and thymus were measured. In the three-vessel tracheal view, diameters of the aortic isthmus and ductus arteriosus were measured. In the aortic arch view, the diameters of the ascending aorta, proximal and distal transverse aortic arches, aortic isthmus, and descending aorta were measured. The HeartAssist™ (Samsung Medison Co. Ltd., Seoul, Republic of Korea) was used for all measurements, which were further modified manually by two experts in fetal echocardiography. We analysed video clips from 350 fetuses and designed scatterplots for each parameter according to GA. The cardiac axis was constant throughout gestation, with a mean value of 37.2°. All other parameters increased gradually with advancing GA. The mean ratios of the left ventricular width and length to the right ventricular width and length were 0.96 and 1.09, respectively. Annular diameters of the aortic valve and pulmonary valve were larger when the valves were closed than when open. We established comprehensive reference ranges for fetal cardiac parameters by using HeartAssist™.