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OBJECTIVE: Our purpose was to establish a reference range of fetal serum β 2 -microglobulin, an index of glomerular filtration rate, and to compare the values obtained in fetuses with urinary tract anomalies with this range. STUDY DESIGN: Serum β 2 -microglobulin was measured in 53 control fetuses at 18 to 39 weeks' gestation and in 14 fetuses with urinary tract anomalies, 9 of which had simultaneous urine sampling. RESULTS: In controls fetal serum β 2 -microglobulin had a mean value of 3.4 mg/L (95% data intervals 2.0 to 4.9) and did not correlate with gestational age. In the 14 fetuses with urinary tract anomalies β 2 -microglobulin levels were increased overall compared with controls (median Z score 1.7, range −0.1 to 9.2), and this was also the case in the five fetuses with unilateral renal disorders (median Z score 1.7, range −0.1 to 3.8) and in a fetus who underwent vesicoamniotic shunting and had normal renal function at birth. Serum β 2 -microglobulin was normal in 4 fetuses with bilateral urinary tract obstruction and normal function at postnatal follow-up and also in 1 of 5 fetuses with renal failure. In fetuses with bilateral uropathy urinary sodium correlated with serum β 2 -microglobulin levels. CONCLUSIONS: Increased values of serum β 2 -microglobulin in fetuses with urinary tract anomalies indicate an impaired glomerular filtration rate. The finding of raised concentrations in fetuses with unilateral damage suggests that the compensatory role of the normal kidney is not complete during intrauterine life. Larger series are required to ascertain whether fetal blood sampling is warranted in the antenatal investigation of renal function, especially in view of the close correlation between urinary sodium and serum β 2 -microglobulin levels in fetuses with bilateral obstruction. (Am J Obstet Gynecol 1997;176:54-7.) more...

Seventy-one fetal urine samples were taken from the bladder or renal pelvis of 33 fetuses at 13-36 weeks' gestation with a diagnosis of urinary tract anomaly. Severe isolated hydronephrosis in the absence of an enlarged bladder was the indication for sampling in 12/33 fetuses (26 samples), who were retrospectively classified into three groups: normal, intermediate, and dysplastic, based on the evaluation of postnatal renal function or histology. For all samples, urinary sodium (Na+), calcium (Ca2+), creatinine, beta 2-microglobulin, and N-acetyl-beta-D-glucosaminidase (NAG) were measured. Among the 71 fetal urine samples, both beta 2-microglobulin and NAG correlated inversely with gestational age, Na+, and Ca2+, but not with creatinine concentrations. However, the correlation of urinary beta 2-microglobulin with gestational age was dependent on the Na+ and Ca2+ concentrations, whereas urinary NAG correlated significantly with urinary Na+ and Ca2+, and also with gestational age. In fetuses with isolated hydronephrosis, only Na+, and not Ca2+, was significantly related to both beta 2-microglobulin and NAG. Only Na+ and beta 2-microglobulin were significantly, and similarly, higher in both dysplastic and intermediate kidneys when compared with fetuses with normal postnatal function. If only the last urine sampled was considered, there was overlapping of all parameters in the three groups. In isolated hydronephrosis, only the most extreme forms of renal failure might be suggested by elevated levels of Na+, Ca2+, beta 2-microglobulin, and NAG, without an obvious superiority of any of these parameters. more...