NPPA and Hypervolemia: These parallel attenuations in “standing ANP versus supine ANP” and “standing SV versus supine SV” as gestation advances may be due to initial physiologic hypervolemia of pregnancy followed by, as gestation advances, increasingly impaired venous return to the right side of the heart via compression of the IVC by the increasingly gravid uterus when supine and relief of this compression upon standing (Sala et al., 1995).