Etiology of third-trimester maternal hyperuricemia in nonpreeclamptic twingestations

Objective: To determine whether the higher maternal serum uric acid levels observed in the third trimester of nonpreeclamptic twin gestations result f rom increased uric acid production or decreased renal excretion. Methods: Thirty-four nonpreeclamptic subjects with twin gestations were ana lyzed, along with 34 singleton controls matched for age, ethnicity, prepreg nancy weight, height, and gestational age. For each subject, a serum sample and 24-hour urine specimen were obtained in the third trimester. Serum and urine uric acid and creatinine levels were determined, as well as total 24 -hour urine uric acid, uric acid clearance, creatinine clearance, fractiona l uric acid clearance, and net tubular uric acid absorption. Results: The twin gestation group had significantly higher maternal serum u ric acid levels (5.2 +/- 1.2 compared with 4.0 +/- 1.0 mg/dL, P < .001) and maternal serum creatinine levels (0.7 +/- 0.2 compared with 0.5 +/- 0.1 mg /dL, P < .001) than the paired singleton group. This was associated with gr eater 24-hour urine uric acid excretion (688.7 +/- 167.0 compared with 597. 7 +/- 164.2 mg, P = .04) and 24-hour urine creatinine excretion (1268.4 +/- 249.9 compared with 1161.2 +/- 277.1 mg, P = .03) in the twin group. No di fferences were seen between the groups in uric acid clearance, creatinine c learance, fractional uric acid clearance, filtered uric acid load, or net u ric acid absorption. Conclusion: The higher maternal serum uric acid levels observed in the thir d trimester of nonpreeclamptic twin gestations result in part from increase d uric acid production, as reflected in the increased daily uric acid excre tion. (Obstet Gynecol 2001;97:62-5) (C) 2001 by The American College of Obs tetricians and Gynecologists.)