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1Division of Nephrology, Department of Medicine, and 2Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, California 94305; and 3Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Submitted 21 May 2003 ; accepted in final form 31 October 2003
We evaluated the glomerular filtration rate (GFR) during the second postpartum week in 22 healthy women who had completed an uncomplicated pregnancy. We used physiological techniques to measure GFR, renal plasma flow, and oncotic pressure and computed a value for the two-kidney ultrafiltration coefficient (Kf). We compared these findings with those in pregnant women previously studied on the first postpartum day as well as nongravid women of reproductive age. Healthy female transplant donors of reproductive age permitted the morphometric analysis of glomeruli and computation of the single-nephron Kf. The aforementioned physiological and morphometric measurements were utilized to estimate transcapillary hydraulic pressure (
P) from a mathematical model of glomerular ultrafiltration. We conclude that postpartum day 1 is associated with marked glomerular hyperfiltration (+41%). A theoretical analysis of GFR determinants suggests that depression of glomerular capillary oncotic pressure, the force opposing the formation of filtrate, is the predominant determinant of early elevation of postpartum GFR. A reversal of the gestational hypervolemia and hemodilution, still evident on postpartum day 1, eventuates by postpartum week 2. An elevation of oncotic pressure in the plasma that flows axially along the glomerular capillaries to supernormal levels ensues; however, GFR remains modestly elevated (+20%) above nongravid levels. An analysis of filtration dynamics at this time suggests that a significant increase in
P by up to 16%, an
50% increase in Kf, or a combination of smaller increments in both must be invoked to account for the persistent hyperfiltration.
pregnancy; glomerular hemodynamics; ultrafiltration coefficient; transcapillary hydraulic pressure gradient
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