Kidney Changes During Pregnancy
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The kidney undergoes
tremendous anatomic and physiologic changes during pregnancy. There is a
significant dilation of the upper urinary tract, primarily due to the mechanical
obstruction of the ureters at the pelvic brim by the enlarged uterus. The
dilatation is facilitated by the high levels of progesterone which is a
smooth muscle relaxant.
Of particular importance is the fact that these anatomic changes may persist
for up to 6 weeks and
may be mistaken for other causes of obstructive uropathy.
In addition to the anatomic change, there is tremendous physiologic change
as manifested by an increase in the glomerular filtration rate of between
40-50% of normal. This parallels the increases in and . It begins
as early as the 8th to 10th week of gestation and is evidenced by a decrease
in the serum creatinine and BUN as well as an increase in the creatinine
clearance. This is the only condition known to medicine that can increase
the glomerular filtration rate that much. The decrease in serum creatinine
and BUN is very important from a clinical standpoint. Pregnant patients
who have a serum creatinine or BUN at the upper limit of normal as defined
by the laboratory for non-pregnant individuals should be viewed with marked
suspicion of renal impairment. The serum creatinine should normally be
below 0.8 mg% and the BUN below 13 mg% in the pregnant patient.
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Plasma concentrations of electrolytes, glucose and urea,
fall if more water than sodium, for example, is retained. Over the whole
period of gestation there is retention of 7.5L of water and 900 mmol of
sodium.
After the 12th week of gestation, progesterone can induce
dilation and atony of the renal calyses and ureters. With advancing gestation,
the enlarging uterus can compress the ureters as they cross the pelvic
brim and cause further dilatation by obstructing flow. These changes may
contribute to the frequency of during pregnancy.
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The information in this page is presented in summarised form and has been taken
from the following source(s):
1.
Robert J. Blaskiewicz, M.D. Clinical Professor, Department of Obstetrics, Gynecology
and Women's Health, Saint Louis University, U.S.A.:
2.
World Anaesthesia & the World Federation of Societies of Anaesthesiologists :
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Introduction
