Effect of fetal number on maternal serum uric acid concentration.

The aim of this study was to examine whether maternal serum uric acid (UA) concentrations are influenced by the number of fetuses and whether this effect is confounded by maternal body mass index (BMI). Medical records of 207 consecutive twin and 69 triplet pregnancies admitted to our high-risk pregnancy unit between 1994 and 1998 were reviewed. Pregnancies complicated by acute or chronic renal diseases, vascular diseases, hypertension, hemolysis, diabetes mellitus, or proteinuria were excluded. The remaining 137 twin and 42 triplet pregnancies were matched with 118 consecutive singleton pregnancies who met the same exclusion criteria and were admitted in the first half of 1998. Each birth order study group was further stratified and compared within three maternal BMI subgroups. Serum UA concentrations were higher in twin and triplet pregnancies compared to singletons (4.6 +/- 1.3, 5.2 +/- 1.2, and 3.8 +/- 0.7 mg%, respectively; p <0.01). These differences in UA concentration persisted after grouping by BMI classes. Serum UA concentration in pregnancy are positively correlated with the number of fetuses. For clinical purpose, the UA cutoff concentration should be adjusted using mean + 2 SD as follows: 5.2, 7.2, and 7.6 for singleton, twin, and triplets, respectively.