Clinical utility of augmentation index as a new parameter of peripheral circulation in human fetuses

Background: Augmentation index (AI) is calculated from the central arterial pressure or pulse waveform and known as a parameter to evaluate arterial vascular function in adults. Patients with deterioration of peripheral circulation will demonstrate increased AI values as well as those with cardiovascular risks. It is because increased AI is caused by the early timing of the reflection wave from the periphery. On the other hand, in fetuses, although arterial pressure waveforms are not available, pulse waveforms of fetal descending aorta are recordable by using an echo-tracking system. Therefore in this study we aimed to evaluate the utility of fetal AI calculated from aortic pulse waveforms for detecting the altered peripheral circulation in human fetuses. Study design: Fetal AI was calculated from pulse waveforms in the descending aorta using an echo-tracking system. In a cross-sectional study of 105 normal fetuses, the reference range was constructed using linear regression analysis. Retrospectively, 36 growth-restricted fetuses were divided into 2 subgroups, normal (n= 21) and increased AIx (n= 15), based on the 90th percentile value of normal fetuses. Clinical parameters were compared using Fisher's exact test or Mann-Whitney U test. Results: Fetal AI decreased linearly with advancing gestational age (r²=0.820). The incidences of umbilical artery absent/reversed end-diastolic flow, brain-sparing effect, and oligohydramnios were significantly higher in the increased AI group than the normal AI group. Conclusion: Fetal AI has a possibility to detect deteriorated peripheral circulation in the fetal body as well as fetoplacental circulation.