Amniotic fluid uric acid and creatinine as measures of fetal maturity
Weiss, R.R.; Duchin, S.; Evans, M.I.; Finkelstein, F.; Mann, L.I.
Obstetrics and Gynecology 44(2): 208-214
1974
ISSN/ISBN: 0029-7844 PMID: 4423245 Document Number: 75889
In the course of diagnostic investigation after the 24th week of pregnancy, or between the 10th and 20th week in case of termination of pregnancy, 111 samples of amniotic fluid were taken by transabdominal amniocentesis. Creatinine was estimated by the Folin-Wu method and autoanalyser; uric acid by Archibald's method. The results are graphed and discussed. Both are expressed in relation to age and weight of the foetus. Creatinine rose significantly to 2.30 plus or minus 0.58 mg/100 ml at 36 weeks and to 2.64 plus or minus 0.68 at 2500 g weight. Uric acid rose steadily to 11.8 plus or minus 2.9 mg/100 ml at 36 weeks and further by an insignificant amount to term. It rose with foetal weight to 12.9 plus or minus 3.9 (r = 0.728) at 2500 g; above 2500 g it fell slightly. Creatinine showed a constant ratio to uric acid: 0.243 plus or minus 0.006 (r = 0.827). Hence creatinine or uric acid reliably indicates foetal age, or the maturity of the foetal kidney, up to 36 weeks or 2500 g weight. Thereafter the relation to weight remains constant.