Amniotic fluid uric acid and creatinine measures of fetal maturity

Uric acid concentrations in amniotic fluid are evaluated throughout pregnancy in 111 normal gravidas (from 10 to 43 weeks’ gestation). In 20 patients, serial determinations were followed, and the amniotic fluid creatinine concentration was also determined in this group Our data indicate that both uric acid and CTeatinine levels in amniotic fluid rise sharply up to the 36th week of gestation or 2500 g of birthweight. With further increase in gestational age or birthweight, both uric acid and creatinine either maintained their peak levels or showed a slight decrease (statistically insignificant). It is con» eluded that a uric acid concentration of 10 mg/100 ml or more in the amniotic fluid would reliably predict a fetal gestational age of 36 weeks in 85% of patients. The parallel behavior of these nitrogenous constituents in the amniotic fluid is discussed and related to the physiologic maturation of the fetal kidney.