Glomerular filtration rate (GFR), measured as 24-h creatinine clearance (Ccr), increases by 6-8 weeks' gestation. Serum creatinine (Scr) and urea (Surea), which average 70 p mol/l and 5 mmol/l, respectively, in non-pregnant women, decrease to mean values of 50 pmol/l and 3 mmol/l during pregnancy. At term a 15-20% GFR decrement occurs, which affects Scr minimally.
An Scr of 80 pmol/l and urea of 6 mmol/l, which are acceptable when non-pregnant, are suspect in pregnancy. Caution is needed, however, when assessing kidney function by Scr alone, especially if some decline in GFR has already accrued because creatinine is both filtered and secreted, with the creatinine clearance:inulin clearance (C cr : Cinulin) ratio usually 1.1-1.2. With the progression of renal dysfunction a greater proportion of urinary creatinine is via secretion with the clearance ratio attaining 1.4-1.6 when Scr > 125 pmol/l. Thus, GFR could be considerably overestimated.
Prediction equations, such as the Cockcroft-Gault (CG) Formula, which use Scr in relation to sex, age and weight to calculate GFR are best avoided in pregnancy because of changing body weight. A relatively new formula, the Modification of Renal Disease 2 (MDRD2) equation excludes weight but it has not yet been validated in pregnancy. Ideally, therefore, evaluation of renal function in pregnancy should be based on Ccr and not Scr. Furthermore, Scr levels may increase up to 17 pmol/l shortly after ingestion of cooked meat (because cooking converts preformed cre-atine to creatinine), which has to be taken into account when timing blood sampling during a 24-h Ccr test.
In normal pregnancy 24-h urinary total protein excretion (TPE) increases and up to 300 mg (some would say 500 mg) can be regarded as normal. So-called significant protein-uria with TPE>300 mg/24 h may correlate with 30 mg/dl in a 'spot urine' but given the problems with dipstick testing, many still prefer a 24-h or some timed quantitative determination. Use of 'spot urine' protein/creatinine ratios >30 mg/pmol is, however, an alternative.
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Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.