Renal function Glomerular filtration rate and renal plasma flow increase ...50%
Maintenance of Decreased bicarbonate threshold; acid-base progesterone stimulates respiratory center osmotic thresholds for AVP release and thirst decrease; hormonal disposal rates increase Size returns to normal postpartum
Can be confused with obstructive uropathy; retained urine leads to collection errors; renal infections are more virulent; may be responsible for "distention syndrome"; elective pyelography should be deferred to at least 12 weeks postpartum
Serum creatinine decreases during normal gestation; >0.8 mg/dL (> 72 �mol/L) creatinine already borderline; protein, amino acid, and glucose excretion all increase
Serum bicarbonate decreased by 4-5 mEq/L; Pc02 decreased 10 mm Hg; a Pc02 of 40 mm Hg already represents CO2 retention 5 mEq/L) during normal gestation; increased placental metabolism of AVP may cause transient diabetes insipidus during pregnancy
AVP = vasopressin; IVP = intravenous pyelography; Pc02= partial pressure carbon dioxide. Modified from Lindheimer, 2000.
elevated GFR persists until term, even though renal plasma flow declines during late pregnancy. Primarily as a consequence of this elevated GFR, approximately 60 percent of nulliparas during the third trimester experience urinary frequency, and 80 percent experience nocturia (F rederice, 2013).
During the puerperium, a marked GFR persists during the first postpartum day, principally from the reduced glomerular capillary oncotic pressure. A reversal of the gestational hypervolemia and hemodilution, still evident on the first postpartum day, eventuates by the second week postpartum (Odutayo, 2012).
Studies suggest that relaxin, discussed earlier (p. 52), may mediate both increased GFR and renal blood flow during pregnancy (Conrad, 2014a; Helal, 2012). Relaxin boosts renal nitric oxide production, which leads to renal vasodilation and lowered renal aferent and eferent arteriolar resistance. This augments renal blood flow and GFR (Bramham, 2016). Relaxin may also increase vascular gelatinase activity during pregnancy, which leads to renal vasodilation, glomerular hyperiltration, and reduced myogenic reactivity of small renal arteries (Odutayo, 2012).
As with blood pressure, maternal posture may considerably inluence several aspects of renal function. Late in pregnancy, the sodium excretion rate in the supine position averages less than half that in the lateral recumbent position. The efects of posture on GFR and renal plasma low vary.
One unusual feature of the pregnancy-induced changes in renal excretion is the remarkably increased amounts of some nutrients lost in the urine. Amino acids and water-soluble vitamins are excreted in much greater amounts (Shibata, 2013).