REN and hydrops fetalis: BP fluctuations are triggered by multiple systems including the renin-angiotensinsystem, baroreflex, myogenic vascular response, and release of nitricoxide.23 Thus, theelevations of the LF and VLF components observed in this study may be related to theincrease in SBP variability through changes in myogenic vascular function.23 The HF component, which appears tobe related to endothelial nitric oxide23, was similar between the groups and did not appear to beinvolved in increased pressure variability.