Of renal function tests, serum creatinine levels decline during normal pregnancy from a mean of 0.7 to 0.5 mg/dL. Values of 0.9 mg/dL or reater sugest underying renal disease and prompt further evaluation. Creatinine clearance in pregnancy averages 30 percent higher than the 100 to 115 mLi min in nonpregnant women. his is a useful test to estimate renal function, provided that complete urine collection is made during an accurately timed period. If this is not done precisely, results are misleading (Lindheimer, 2000, 2010). During the day, pregnant women tend to accumulate water as dependent edema, and at night, while recumbent, they mobilize this fluid with diuresis. This reversal of the usual nonpregnant diurnal pattern of urinary flow causes nocturia, and urine is more dilute than in nonpregnant women. Failure of a pregnant woman to excrete concentrated urine after withholding fluids for approximately 18 hours does not necessarily signiy renal damage. In fact, the kidneys in these circumstances function perfectly normally by excreting mobilized extracellular fluid of relatively low osmolality.
Glucosuria during pregnancy may not be abnormal. The appreciably increased GFR, together with impaired tubular reabsorptive capacity for filtered glucose, accounts for most cases of glucosuria. Chesley (1963) calculated that about a sixth of pregnant women will spill glucose in the urine. hat said, although common during pregnancy, when glucosuria is identiied, a search for diabetes mellitus is pursued.
Hematuria frequently results from contamination during collection. If not, it most often suggests urinary tract disease or infection. Hematuria is common after diicult labor and delivery because of trauma to the bladder and urethra.
Proteinuria is typically deined in nonpregnant subjects as a protein excretion rate of more than 150 mg/ d. Because of the aforementioned hyperiltration and possible reduction of tubular reabsorption, proteinuria during pregnancy is usually considered signiicant once a protein excretion threshold total protein excretion by gestational age. Mean and 95-percent confidence limits are outlined. (Redrawn from Higby K, Suiter CR,
Phelps JY, et al: Normal values of urinary albumin and total protein excretion during pregnancy. Am J Obstet Gynecol 171 :984, 1994.) of at least 300 mg/d is reached (Odutayo, 2012). Higby and coworkers (1994) measured protein excretion in 270 normal women throughout pregnancy (Fig. 4-14). Mean 24-hour excretion for all three trimesters was 11i5 mg, and the upper 95-percent conidence limit was 260 mg/d without significant diferences by trimester. They showed that albumin excretion is minimal and ranges from 5 to 30 mg/d. Proteinuria increases with gestational age, which corresponds with the peak in CFR (see Fig. 4-13)(Odutayo, 2012).
Measuring Urine Protein. The three most commonly employed approaches for assessing proteinuria are the qualitative classic dipstick, the quantitative 24-hour collection, and the albumin/ creatinine or protein/creatinine ratio of a single voided urine specimen. he pitfalls of each approach have been reviewed by Conrad (20 14b) and Bramham (2016) and their colleagues. he principal problem with dipstick assessment is that it fails to account for renal concentration or dilution of urine. For example, with polyuria and extremely dilute urine, a negative or trace dipstick could actually be associated with excessive protein excretion.