Renal Hemodynamics: Longitudinal Study from the Late Fetal Life to One Year of Age

>Objective: To evaluate longitudinally the renal circulation from late gestation to the first year of life in order to understand fundamental changes within this vascular bed as the fetus adapts to major circulatory changes occurring during this time period.
Methods: Sixteen healthy human fetuses were studied during the last trimester of the pregnancy, within 2 days of birth, at 6 weeks, at 6 months, and at 1 year. Using noninvasive color pulsed Doppler, blood flow velocities of the renal artery, the tricuspid and mitral valves in the fetus, and in the ascending aorta in the newborn/infants were obtained at each study. Diameters of these respective areas were also obtained. Total cardiac output and renal blood flow were calculated using the time velocity integral, the area of the structure of interest, and heart rate.
Results: 1) Renal artery dimensions, time velocity integral, peak flow velocity, systolic to diastolic ratio, absolute volume blood flow (RVBF) were all significantly correlated with advancing gestational age; 2) RVBF relative to body weight and percent RVBF were not.Conclusions: In spite of an overall increase in renal blood flow, flow to the kidney appears to be constant during the time period of this study. Most of the "maturational" changes that occur within this vascular bed appear to be related to changes within the vascular resistance and the renal artery diameter.